Light-triggered diamond switches

Abstract

A system includes a power transistor having an insulating diamond substrate and a set of ohmic contacts disposed on or above the insulating diamond substrate to receive current. A light source is configured to inject, into the insulating diamond substrate, an optical signal having a wavelength designed to turn on the power transistor.

Description

Attorney Docket No.: 30831.107 (L0103PCT)LIGHT-TRIGGERED DIAMOND SWITCHESTECHNICAL FIELD

[0001] Embodiments of the disclosure relate generally to high-power transistors, and more specifically, relate to light-triggered diamond switches.BACKGROUND

[0002] Power outages cost American households $150 billion annually. For instance, weather-related outages alone account for $25 billion to $70 billion per year, affecting half a million Americans on average daily. To reach the 2050 goal of a more reliable, resilient, and net zero grid, faster and higher power electronic devices with improved protection and simpler controls are needed.

[0003] The Department of Energy of the U.S. Government, for example, wants fast control switches (ON / OFF) for high-power delivery systems, e.g., power grids. Sometimes disruptions to the power grid in one state cause a house or building in another state (or perhaps multiple states away) to also lose power. The U.S. Government therefore wants to isolate the power system within each individual state from that of each other state, e.g., so that each state may operate as an island in terms of grid isolation. High-power switches or transistors need to be able to simultaneously handle high amounts of power and be fast switching. None of the power electronics today can handle this kind of speed with grid power levels.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] A more particular description of the disclosure briefly described above will be rendered by reference to the appended drawings. Understanding that these drawings only provide information concerning typical embodiments and are not therefore to be considered limiting of its scope, the disclosure will be described and explained with additional specificity and detail through the use of the accompanying drawings.

[0005] FIG. 1 is a schematic block diagram of a system or device employing a light- triggered diamond switch, e.g., a diamond photoconductive semiconductor switch (PCSS), according to various embodiments.

[0006] FIGs. 2A-2B are cross-sectional views of a lateral diamond PCSS, according to at least some embodiments.Attorney Docket No.: 30831.107 (L0103PCT)

[0007] FIGs. 3A-3B are cross-sectional views of a vertical diamond PCSS, according to at least some embodiments.

[0008] FIG. 4A is an image of an electrical connection design of a chipset that incorporates one or more diamond PCSS devices as discussed herein, according to various embodiments.

[0009] FIG. 4B is an image of a top view of multiple diamond PCSS devices instantiated on a single insulating diamond substrate, according to some embodiments.

[0010] FIG. 4C is a block diagram depiction of the ohmic contacts employed in the multiple diamond PCSS devices of FIG. 4A according to at least one embodiment.

[0011] FIG. 5 is a schematic diagram of a PCSS optical experimental setup used to test the diamond PCSS devices illustrated herein according to some embodiments.

[0012] FIG. 6 is a graph illustrating a laser signal that triggers a diamond PCSS device and a resultant voltage response of the diamond PCSS device according to some embodiments.

[0013] FIG. 7A is a graph of oscilloscope voltage data for an 8 micrometer (pm) contact separation at different wavelengths according to some embodiments.

[0014] FIG. 7B is a graph of a diamond PCSS peak ON-current for the 8 pm contact separation at different wavelengths according to some embodiments.

[0015] FIG. 8A is a graph of oscilloscope load voltage data for the 8 pm contact separation at different laser power outputs according to some embodiments.

[0016] FIG. 8B is a graph of oscilloscope load voltage data for a first 50 pm contact separation at different laser power outputs according to some embodiments.

[0017] FIG. 8C is a graph of oscilloscope load voltage data for a second 50 pm contact separation at different laser power outputs according to some embodiments.

[0018] FIG. 8D is a graph of oscilloscope load voltage data for a 100 pm contact separation at different laser power outputs according to some embodiments.

[0019] FIG. 9 is a graph of diamond PCSS peak ON-current for four devices at different laser power output levels according to some embodiments.

[0020] FIG. 10A is a graph of oscilloscope load voltage for an 8 pm contract separation at different applied biases according to some embodiments.

[0021] FIG. 10B is a graph of oscilloscope load voltage for a first 50 pm contact separation at different applied biases according to some embodiments.Attorney Docket No.: 30831.107 (L0103PCT)

[0022] FIG. 10C is a graph of oscilloscope load voltage for a second 50 pm contact separation at different applied biases according to some embodiments.

[0023] FIG. 10D is a graph of oscilloscope load voltage for a 100 pm contact separation at different applied biases according to some embodiments.

[0024] FIG. 11A is a graph of diamond PCSS peak ON-current for 8 pm and 50 pm contact separation at different applied biases with a laser wavelength of 220 nanometers (nm) and a 50 microjoule (pJ) output according to some embodiments.

[0025] FIG. 11B is a graph of diamond PCSS peak ON-current for 8pm and 50pm contact separation at different applied biases with a laser wavelength of 210 nm and a 40 pJ output according to some embodiments.

[0026] FIG. 12A is a graph of peak photocurrent density versus electric field for a diamond PCSS versus gallium nitride (GaN) and 6-hexagonal, silicon carbide (6H-SiC) according to some embodiments.

[0027] FIG. 12B is a graph of ON / OFF ratio versus energy per laser pulse for a diamond PCSS versus gallium nitride (GaN) and 6-hexagonal, silicon carbide (6H-SiC) according to some embodiments.

[0028] FIG. 13 is a graph illustrating peak photocurrent density (A / cm) versus DC bias voltage (V) applied to disclosed diamond PCSSs according to some embodiments.

[0029] FIG. 14 is a graph illustrating benchmark of the disclosed diamond PCSS devices compared to previous reported diamond PCSS devices according to some embodiments.

[0030] FIG. 15 is a flowchart of a method for manufacturing the diamond PCSS device or system, in accordance with one or more embodiments of the present disclosure.

[0031] While embodiments of the present disclosure are susceptible to various modifications and alternative forms, exemplary embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description of exemplary embodiments is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the in accordance with one or more embodiments of the present disclosure.DETAILED DESCRIPTION

[0032] The technology now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the disclosure may be embodied in many different forms and should not be construed as limitedAttorney Docket No.: 30831.107 (L0103PCT) to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0033] Likewise, many modifications and other embodiments of the technology described herein will come to mind to one of skill in the art to which the disclosure pertains having the benefit of the teachings presented in the enclosed descriptions and the associated drawings. Therefore, it is to be understood that the disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0034] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art to which embodiments described herein pertain. Although any methods and materials similar to or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the preferred methods and materials are described herein.

[0035] A photoconductive semiconductor switch (PCSS) is a device that uses light (usually from a laser) to control the conduction state of a semiconductor. This works by using the light to generate charge carriers (electrons and holes) in the semiconductor, thereby lowering the resistance of the semiconductor and allowing current to flow. Such PCSS devices are understood to have two states, including ON and OFF. In an OFF state, when there is no light on the semiconductor, the semiconductor has a high resistance, and only a small leakage current can flow. In an ON state, when light shines on the semiconductor, electron-hole pairs are created. The sudden increase in charge carriers reduces the resistance of the semiconductive material, allowing a large current to flow.

[0036] Such PCSS devices have several characteristics beneficial to high-power grid structures, including ultrafast switching times. For example, the transition from high to low resistance can occur in picoseconds (e.g., 10'12seconds) or less, allowing for very fast switching of electrical signals. Further, such PCSS devices exhibit high power handling. Because PCSS devices can handle high voltages and currents, PCSS devices can be used to switch large amounts of power, e.g., hundreds of kilovolts (kV). Additionally, such PCSS devices exhibit a low ON-state resistance. For example, when the PCSS device is on, the PCSS device has a very low resistance, which can improve energy efficiency by reducing power losses when current flows through the PCSS device.Attorney Docket No.: 30831.107 (L0103PCT)

[0037] In addition to these advantages, diamond-based PCSS devices offer optical triggering and electromagnetic isolation against planned or unplanned grid outages and extreme weather disruption, thus addressing the above deficiencies in present power grid switching infrastructure. The present disclosure proposes a fundamental change in intrinsic grid protection by creating a high-voltage, high-current diamond PCSS to actively limit faults to a nominal value. This is made possible in various embodiments via the disclosed power transistor or diamond PCSS switch having an insulating diamond substrate and a set of ohmic contacts disposed on or above the insulating diamond substrate to receive current, e.g., to pass current from one part of a power grid to another part of the power grid. In some embodiments, a system that includes such a power transistor further includes a light source configured to inject, into the insulating diamond substrate, an optical signal having a wavelength designed to turn ON the power transistor or diamond PCSS switch. In some embodiments, the disclosed power transistor is to operate in a low-to-no-defect and low doping region of diamond (i.e., indirect bandgap material) that avoids “lock on,” which is associated with either a direct bandgap PCSS material or large density defects that keep conducting current even after a light source is turned off (or the optical signal from the light source is disconnected).

[0038] Therefore, advantages of the systems and methods implemented in accordance with some embodiments of the present disclosure include, but are not limited to, meeting the highest possible standards (e.g., in terms of high power, fast switching, high OFF resistance, low ON resistance, among others) of a PCSS device for electrical grid delivery of high power. These highest possible standards are made possible by intrinsic, unintentionally doped, or very lightly doped diamond-grown layers acting as substrate and / or other layers of a diamond-based PCSS device. Other advantages will be apparent to those skilled in the art of PCSS design and fabrication, which will be discussed hereinafter.

[0039] FIG. 1 is a schematic block diagram of a system 100 (or device) employing a light-triggered diamond switch, e.g., a diamond photoconductive semiconductor switch (PCSS) 120 or similar power transistor, according to various embodiments. For example, in some embodiments, the system 100 includes a light source 110, which is powered by a power supply 130, and the PCSS 120. In some embodiments, the light source 110 is configured (and aimed) to inject, into an insulating diamond substrate of the diamond PCSS 120, an optical signal 115 having a wavelength designed to turn on the PCSS 120. In some embodiments, the wavelength of the light (e.g., optical signal) is no longer than the bandgap of diamond, e.g.,Attorney Docket No.: 30831.107 (L0103PCT) approximately 5.47 eV, or about 226 nm. In some embodiments, the light source 110 generates different wavelengths and a separate light converter (not illustrated) converts those different wavelengths to 226 nm or above, as will be discussed.

[0040] The diamond PCSS 120 will also be alternatively referred to as a diamond PCSS device herein, e.g., that includes various functional components to operate within the system 100. For example, the diamond PCSS device may include a lead attached to a top ohmic contact and a lead attached to a bottom ohmic contact for being connected to a high-voltage source such as a high-power supply from an electrical grid (see FIGs. 4A-4C). In some embodiments, the power supply 130 is separate or transformed from the electrical grid and is configured to drive the light source 110 in a controlled fashion.Table 1Attorney Docket No.: 30831.107 (L0103PCT)

[0041] Table 1 is a summary of materials that can be used in PCSS devices so that the qualities and benefits of employing diamond as at least the substrate material in a PCSS can be compared with employing other materials that are common in industry. As can be observed, diamond has the largest bandgap, allowing direct current (DC) as opposed to pulsed charging of the PCSS, has the highest thermal conductivity, the highest electron and hole mobility (e.g., low ON-resistance), the lowest electron hole mobility asymmetry (e.g., uniform bipolar transport), indirect bandgap nature (e.g., no lock on), the largest critical electric field (e.g., high voltage operation), and is highly reliable. The bandgap of a material is generally the energy difference between the top of its valence band to the bottom of its conduction band. Due to the large bandgap, diamond is resistant to electromagnetic interference (EMI), which means resilience to EMI attacks and nearby electrical noise, in contrast to silicon for example, which is susceptible to noise and attack.

[0042] In various embodiments, diamond used as a PCSS material also enables uniform current throughout the bulk material. Filamenting (e.g., very high current density paths, such as several mega-amp (MA) / cm2, with diameters of 15-300 pm) is damaging, commonly attributed to the light-induced carrier multiplication, and observed in direct bandgap PCSS such as Indium Phosphide (InP), Gallium Arsenide (GaAs), and Gallium Nitride (GaN). Filamenting, however, is not observed in indirect bandgap materials such as silicon (Si), some silicon carbides (e.g., 6H-SiC), and diamond. Direct bandgap materials can also enter operations of so called “lock-on,” where the PCSS material keeps conducting current even after the light source 110 is turned off (or the optical signal from the light source 110 is disconnected). Indirect bandgap materials, including diamond, however, do not have this lock-on effect unless highly defective, enabling fast and repetitive switching of high power levels.

[0043] In various embodiments, the diamond material employed in the PCSS 120 (or associated devices of power systems) does not use impurities, e.g., is as intrinsic as possible, although could incur unintentional doping or very low doping such that the diamond material can be generally considered an “insulating” diamond substrate. In these embodiments, the PCSS 120 promises fast triggering (e.g., in nanosecond range) and linear current scaling with increasing light intensity from the light source 110, as will be illustrated and discussed in more detail.

[0044] FIGs. 2A-2B are cross-sectional views of a lateral diamond PCSS 200 A or 200B (or lateral diamond PCSS device), respectively, according to at least some embodiments. InAttorney Docket No.: 30831.107 (L0103PCT) some embodiments, the lateral diamond PCSS 200A of FIG. 2A is the PCSS 120 of FIG. 1. In these embodiments, the lateral diamond PCSS 200A includes an insulating diamond substrate 202, a selectively-grown, positive p-type diamond layer 206A and 206B, and a set of ohmic contacts 210A and 210B disposed on (e.g., in physical contact with) the positive p- type diamond layer 206A and 206B, respectively. In some embodiments, the set of ohmic contacts 210A and 210B is disposed directly on (e.g., in physical contact with) the insulating diamond substrate 202.

[0045] In at least some embodiments, the positive p-type diamond layer 206A and 206B is regrown p+ diamond that is highly doped, e.g., with boron or other suitable p+ dopant, via microwave plasma chemical vapor deposition (MPCVD). In various embodiments, the regrown p+ diamond of the positive p-type diamond layer 206A and 206B is performed via a high pressure and high temperature growth process. In some embodiments, the positive p- type diamond layer 206A and 206B is relatively thin, e.g., between 0.5 and 3.0 pm thick. Where the positive p-type diamond layer 206A and 206B is employed, the resistance to current flow through the set of ohmic contacts 210A and 210B, which are made of metal, is reduced for more efficient power transfer.

[0046] In some embodiments, the set of ohmic contacts 210A and 210B is a pair of interdigitated electrodes, e.g., having multiple interdigitated electrode fingers or sets of electrode fingers. For example, interdigitated electrodes are able to increase the amount of current in a lateral PCSS and to receive light efficiently in a vertical PCSS. In either case, employing interdigitated electrodes improves performance of the diamond PCSS devices.

[0047] In disclosed embodiments, illuminating or irradiating light or an optical signal may refer to light from an optical source, which comes into and is absorbed by the diamond substrate. Ohmic contacts 210A and 210B, under a voltage bias, collect the carriers (electrons or holes) and current passes through the insulating diamond substrate 202. In the system 100 (or device) that employs the PCSS 200A, according to some embodiments, the PCSS 200A is to operate in an above-bandgap region of diamond. In some embodiments, a wavelength of an optical signal from the light source 110 is made to be shorter than or equal to 224 nm. In some embodiments, the wavelength of the optical signal 115 from the light source 110 is configured to be approximately 222-223 nm.

[0048] In various embodiments, the insulating diamond substrate 202 is a singlecrystalline diamond material or structure. In some embodiments, the insulating diamond substrate 202 is a Type lb or Type Ila high pressure, high temperature (HPHT) diamondAttorney Docket No.: 30831.107 (L0103PCT) material that is polished on both sides. Type lb diamond material contains isolated nitrogen impurities. This type of diamond is less common in natural diamonds but can be created synthetically, absorbs green light, and generally appears yellow. Type Ila diamond material does not have intentional dopants and contains few impurities. Further, the HPHT process of growing diamond endeavors to replicate the natural conditions under which diamonds form in the Earth’s mantle. The high pressure and high temperature cause the carbon atoms to crystallize and form a diamond structure. In some embodiments, the insulating diamond substrate is between 400 and 600 micrometers (pm) in thickness.

[0049] In at least embodiments, the lateral diamond PCSS 200B of FIG. 2B is similar to the lateral diamond PCSS 200A, but also includes an insulating diamond layer 204 grown as a homoepitaxial layer on the insulating diamond substrate 202. A homoepitaxial layer refers to the process of growing a crystalline layer on a crystalline substrate of the same type. Homoepitaxial growth is often used to form high-quality semiconductor layers with minimal defects because the crystal structure of the layer matches that of the substrate. In some embodiments, the insulating diamond layer 204 is unintentionally doped with thickness less than approximately 3-6 pm. Minimal boron doping and nitrogen compensation may be employed within the insulating diamond layer 204.

[0050] In these embodiments, the insulating diamond layer 204 is between 0.1% and 20% the thickness of the insulating diamond substrate 202. In some embodiments, the insulating diamond layer 204 is less than 5 pm thick. Further, in these embodiments, the set of ohmic contacts 210A and 210B (or the positive p-type diamond layer 206A and 206B, where used) is disposed on (e.g., in physical contact with) the insulating diamond layer 204, as illustrated in FIG. 2B

[0051] FIGs. 3A-3B are cross-sectional views of a vertical diamond PCSS 300A and 300B (or vertical diamond PCSS device), respectively, according to at least some embodiments. FIGs. 3A-3B can also be understood to be partial cross-sectional views of a vertical diamond PCSS or an entire cross-section of the embodiment including the horizontal repetition of FIGs. 3A-3B in some embodiments. In some embodiments, the vertical diamond PCSS 300A of FIG. 3A is the PCSS 120 of FIG. 1. In these embodiments, the vertical diamond PCSS 300A includes an insulating diamond substrate 302, a selectively- grown, positive p-type diamond layer 306 A and 306B, and one or more ohmic contacts 310A and 310B made of metal and disposed on the positive p-type diamond layer 306A and 306B. In some embodiments, the one or more ohmic contacts 310A and 310B include a gapAttorney Docket No.: 30831.107 (L0103PCT) therebetween through which the optical signal 115 (or light) from the light source 110 can be injected. In some embodiments, the ohmic contacts 310A and 310B are disposed directly on a first side of the insulating diamond substrate 302.

[0052] In these embodiments, the vertical diamond PCSS 300A further includes a metal plate electrode 313 disposed on a second side of the insulating diamond substrate 302, opposite to the one or more ohmic contacts 310A and 310B. In some embodiments, the vertical diamond PCSS 300A includes a positive p-type diamond layer 312 disposed on (e.g., in physical contact with) the second side of the insulating diamond substrate 302 and the metal plate electrode 313 is disposed on top of (e.g., in physical contact with) the positive p- type diamond layer 312. In these embodiments, the metal plate electrode 313 enables passing current through the thickness (e.g., the entire depth) of the insulating diamond substrate 302 between the ohmic contacts 310A and 310B and the metal plate electrode 313.

[0053] Thus, in at least some embodiments, as explained (and illustrated in FIGs. 3A- 3B), the vertical diamond PCSS 300A includes at least a first ohmic contact disposed on the first side of the insulating diamond substrate 302 and at least a second ohmic contact disposed on the second side of the insulating diamond substrate 302 opposite from the first ohmic contact. The vertical diamond PCSS 300A further includes selectively-grown, positive p-type diamond layers positioned between the insulating diamond substrate and each of first and second ohmic contacts.

[0054] In some embodiments, the ohmic contacts 310A and 310B are a pair of interdigitated electrodes, e.g., having multiple interdigitated electrode fingers or sets of electrode fingers. In this case, the entire device includes the repetition of FIGs. 3A-3B. In some embodiments, gaps between first electrode fingers (e.g., of the ohmic contacts 310A and 310B) are sized to allow (or enable) a wavelength of the optical signal 115 from a light source of shorter than or equal to 224nm to pass through a thickness of the insulating diamond substrate 302. Thus, in some embodiments, a longer wavelength of light may be required so that the optical signal 115 passes completely through the thickness of the insulating diamond substrate 302.

[0055] In some embodiments, the positive p-type diamond layers 306 A and 306B are selectively grown p+ diamond and highly doped on the first side of the insulating diamond substrate 302, as was discussed with referenced to the positive p-type diamond layer 206A and 206B (FIGs. 2A-2B). In some embodiments, the positive p-type diamond layer 312 is uniformly grown p+ diamond and highly doped on the second side of the insulating diamondAttorney Docket No.: 30831.107 (L0103PCT) substrate 302. In some embodiments, the insulating diamond substrate 302 is between 200 and 500 pm in thickness. In some embodiments, the insulating diamond substrate 302 is a single-crystalline material, e.g., a Type Ila or Type lb material. In other embodiments, the insulating diamond substrate 302 is a single-crystalline Type Ila HPHT diamond material that is polished on both sides. Type Ila diamond material contains very few or no nitrogen impurities and is used for high-quality diamond substrates due to their purity.

[0056] In some embodiments, the vertical diamond PCSS 300B of FIG. 3B is the PCSS 120 of FIG. 1. In various embodiments, the vertical diamond PCSS 300B includes an insulating diamond substrate 302, a selectively-grown, positive p-type diamond layer 306A, 306B, 306C disposed on (e.g., in physical contact with) the first side of the insulating diamond substrate 302, and a selectively-grown, positive p-type diamond layer 306D, 306E, and 306F disposed on (e.g., in physical contact with) the second side of the insulating diamond substrate 302 opposite from the positive p-type diamond layer 306A, 306B, 306C, respectively. In these embodiments, the vertical diamond PCSS 300B further includes ohmic contacts 310A, 310B, 310C made of metal and disposed on the positive p-type diamond layers 306A, 306B, and 306C, respectively. In these embodiments, the vertical diamond PCSS 300B further includes ohmic contacts 310D, 310E, 310F made of metal and disposed on the positive p-type diamond layer 306D, 306E, and 306F, e.g., and opposite from the ohmic contacts 310A, 310B, and 310C, respectively.

[0057] In some embodiments, the ohmic contacts 310A, 310B, and 310C are a set of interdigitated electrodes, e.g., having multiple interdigitated electrode fingers or sets of electrode fingers. In some embodiments, the ohmic contacts 310D, 310E, and 31 OF are a set of interdigitated electrodes, e.g., having multiple interdigitated electrode fingers or sets of electrode fingers. In some embodiments, gaps between first electrode fingers (e.g., of the ohmic contacts 310A, 310B, 310C and corresponding ohmic contacts 310D, 310E, 31 OF) are sized to allow a wavelength of the optical signal 115 from a light source of shorter than or equal to 224 nm to pass through a thickness of the insulating diamond substrate 302. Thus, in some embodiments, a longer wavelength of light may be required so that the optical signal 115 passes completely through the thickness of the insulating diamond substrate 302. In some embodiments, the positive p-type diamond layers 306A, 306B, 306C are selectively grown p+ diamond and highly doped on the first side of the insulating diamond substrate 302, as was discussed with referenced to the positive p-type diamond layer 206A and 206B (FIGs. 2A-2B). Similarly, in some embodiments, the positive p-type diamond layers 306D, 306E,Attorney Docket No.: 30831.107 (L0103PCT)306F are selectively grown p+ diamond and highly doped on the second side of the insulating diamond substrate 302.

[0058] In some embodiments, the insulating diamond substrate 302 is between 200 and 500 pm in thickness. In at least some embodiments, the insulating diamond substrate 302 is a single-crystalline material. In other embodiments, the insulating diamond substrate is a single-crystalline Type Ila HPHT diamond material that is polished on both sides. In some embodiments, structure of the lateral and vertical diamond PCSS devices are summarized, by way of example only, in Table 2 below. These diamond PCSS devices may sustain high current (greater than 10A for a single device) in the ON state with a relatively low impedance under a relatively low peak optical power intensity (less than 500 kW / cm2). Further, these diamond PCSS devices are capable of being switched OFF by turning the optical flux off even in the presence of the high voltage being applied.Table 2

[0059] FIG. 4A is an image of an electrical connection design of a chipset 400 that incorporates one or more diamond PCSS devices 401 as discussed herein, according to various embodiments. In disclosed embodiments, the chipset 400 is employed for purposes of testing different-sized diamond PCSS devices 401. In some embodiments, a plurality of lead lines 405 connect pads of a chip having the PCSS devices 401 to pins that lead to off-chip lines 409, e.g., to be connected to off-chip components. In this embodiment, there are 17 pins on each side (e.g., T1-T17, L1-L17, and R1-R17), although different numbers of pins is envisioned as well. The bottom row of pins is unused and is thus not labeled.

[0060] FIG. 4B is an image of a top view of multiple diamond PCSS devices instantiated on a single insulating diamond substrate 402, according to some embodiments. The multipleAttorney Docket No.: 30831.107 (L0103PCT)PCSS devices can be formed from multiple ohmic contacts 410 that are spaced from each other by different-sized gaps. Each ohmic contact 1410 includes lead lines 411 used to pass current to or receive current from the single insulating diamond substrate 402.

[0061] FIG. 4C is a block diagram depiction of the ohmic contacts 410 employed in the multiple diamond PCSS devices of FIG. 4A according to at least one embodiment. Note the different sizes of the respective ohmic contacts 410, which are labeled with the corresponding pins to which each respective ohmic contact 410 is connected for testing. Prior to testing, a dark resistance at +40V / -40V for four diamond PCESS devices was measured as follows: 1) L6-R7 (50 pm): measured greater than 10 GQ; 2) R7-R5 (50 pm) measured greater than 10 GQ; 3) L8-L7 (8 pm) measured 236 MQ; and 4) L7-L9 (100 pm) measured at greater than 10 GQ

[0062] FIG. 5 is a schematic diagram of a PCSS optical experimental setup 500 used to test the diamond PCSS devices illustrated in FIGs. 4A-4C according to some embodiments. In these embodiments, the setup 500 includes an oscilloscope 505 (with a 1 MQ and 13 pF coupling). The 40V power source is passed through the PCSS 520 (or PCSS device), which is triggered ON / OFF by the optical signal 115 from a laser source 510. In these embodiments, a silicon photodiode 515 is employed to detect the optical signal 115 and trigger the oscilloscope 505 to record output responses of the PCSS 520, which will be discussed in more detail hereinafter. A load voltage (VL) can also be measured across a 500 kQ resistance.

[0063] In these embodiments, a wavelength-dependent response was recorded using wavelengths that varied as follows: 210 nm, 212 nm, 214 nm, 216 nm, 218 nm, 219 nm, 220 nm, and 221 nm. Fixed laser powers were approximately 400 ±50 pm for spot size of 2 mm by 2 mm. These parameters were used to test four devices having 8 pm, 50 pm, and 100 pm gap sizes (between the ohmic contacts).

[0064] In these embodiments, a laser power-dependent response was recorded, which was obtained at a fixed wavelength of 220 nm of the optical signal 115. In this experiment, the laser beam power varied from 150 pW to 500 pW. These parameters were used to test four devices having 8 pm, 50 pm, and 100 pm gap sizes.

[0065] In these embodiments, an electric field-dependent response was recorded using a fixed wavelength of the optical signal 115 of 210 nm, 220 nm, and a fixed power at 500 pW. Applied bias varied from 0.5 V to 40 V and was tested on two devices having 8 pm and 50 pm gap sizes.Attorney Docket No.: 30831.107 (L0103PCT)

[0066] FIG. 6 is a graph illustrating a laser signal that triggers the diamond PCSS device 520 and a resultant voltage response of the diamond PCSS device according to some embodiments. This transient response from the laser source 510 and the diamond PCSS device 520 was for a 50 pm contact separation. Results of this initial optical response from the diamond PCSS 520 are summarized in Table 3. Note that the transient response measurement of the diamond PCSS 520 is limited by a bandwidth of the oscilloscope 505 used to measure the responses.Table 3

[0067] FIG. 7A is a graph of oscilloscope voltage data for an 8 micrometer (pm) contact separation at different wavelengths (see FIG. 5) according to some embodiments. FIG. 7B is a graph of a diamond PCSS peak ON-current for the 8 pm contact separation at different wavelengths according to these embodiments.

[0068] FIG. 8A is a graph of oscilloscope load voltage data for the 8 pm contact separation at different laser power outputs according to some embodiments. FIG. 8B is a graph of oscilloscope load voltage data for a first 50 pm contact separation at different laser power outputs according to some embodiments. FIG. 8C is a graph of oscilloscope load voltage data for a second 50 pm contact separation at different laser power outputs according to some embodiments. FIG. 8D is a graph of oscilloscope load voltage data for a 100 pm contact separation at different laser power outputs according to some embodiments. As can be observed, an increase in laser power output increases the voltage level output through the diamond PCSS 520.

[0069] FIG. 9 is a graph of diamond PCSS peak ON-current for four devices at different laser power output levels according to some embodiments. As can be observed, approximately linear responses are obtainable between the laser power output and the current (measured in mA) flowing through the diamond PCSS 520. When other composite materials are used instead of diamond, the ON current scaling is limited due to current density, whichAttorney Docket No.: 30831.107 (L0103PCT) eventually saturates absorption ability of the PCSS device. The disclosed diamond PCSS device 520, however, does have such a limit due to using an insulating or intrinsic diamond material and having the entire bandgap of diamond available, enabling further current scaling.

[0070] FIG. 10A is a graph of oscilloscope load voltage for an 8 m contract separation at different applied biases according to some embodiments. FIG. 10B is a graph of oscilloscope load voltage for a first 50 pm contact separation at different applied biases according to some embodiments. The experiments associated with FIGs. 10A-10B included a 220 nm optical signal from the laser source 510 and 50 pJ laser power output.

[0071] FIG. 10C is a graph of oscilloscope load voltage for a second 50 pm contact separation at different applied biases according to some embodiments. FIG. 10D is a graph of oscilloscope load voltage for a 100 pm contact separation at different applied biases according to some embodiments. The experiments associated with FIGs. 10C-10D included a 210 nm optical signal from the laser source 510 and 40 pJ laser power output

[0072] FIG. 11A is a graph of diamond PCSS peak ON-current for 8 pm and 50 pm contact separation at different applied biases with a laser wavelength of 220 nm and a 50 pJ output according to some embodiments. FIG. 11B is a graph of diamond PCSS peak ON- current for 8 pm and 50 pm contact separation at different applied biases with a laser wavelength of 210 nm and a 40 pJ output according to some embodiments. Again note the generally linear responses (ON-current versus e-field strength) in each of these experiments.

[0073] FIG. 12A is a graph of peak photocurrent density (A / cm) versus electric field (V / cm) for a diamond PCSS versus gallium nitride (GaN) and 6-hydrogen, silicon carbide (6H-SiC) according to some embodiments. FIG. 12B is a graph of ON / OFF ratio versus energy per laser pulse (in mJ) for a diamond PCSS versus gallium nitride (GaN) and 6- hydrogen, silicon carbide (6H-SiC) according to some embodiments. Although the diamond PCSS devices fabricated for purposes of these experiments are discussed having particular dimensions and parameters, others are envisioned and these are illustrated only by way of example of proof of functionality in some, specific implementations.

[0074] In the experiments performed that generated the graphs of FIGs. 12A-12B, diamond PCSS structures with ohmic contact (or electrode) spacings of 8 pm, 50 pm, and 100 pm were fabricated. The lateral PCSS devices were based on a 500 pm thick, 4 x 4mm2Type Ila high-pressure, high-temperature (HPHT) diamond substrate. In some embodiments, a 500 nm-thick layer of heavily boron-doped p+diamond with atomic doping concentration of 5 x 1O20cm’3was grown (as the insulating diamond substrate 202 or 302) on which a 1.5 pmAttorney Docket No.: 30831.107 (L0103PCT) thick layer of unintentionally doped layer (e.g., labeled as 206x in the Figures) was grown using MPCVD. In some embodiments, the p+diamond layer 206A and 206B has a sheet resistance of 41.4 Q / n and serves as the low-resistivity channel between electrodes.Rectangular ohmic metal contacts (e.g., labeled as 210x and 310x in the Figures) may be composed of titanium (Ti) (e.g., 30 nm), platinum Pt (e.g., 30 nm), or gold (Au) (e.g., 100 nm) deposited by e-beam evaporation, followed by thermal annealing at 450°C in an ambient of argon gas.

[0075] Photoconductive measurements of the diamond PCSS devices were carried out using a tunable optical parametric oscillator (OPO) laser (e.g., the laser source 510) in the spectral range of 210-226 nm with laser pulse width of 5 ns. The laser spot size was fixed to a diameter of 2 mm using an aperture to keep the laser power density uniform, and the laser spectral width is below 0.1 nm. The optical power output was fixed to 40 pj / pulse, which corresponds to a laser power density of 252 kW / cm2and total energy of 10 nJ, 127 nJ, and 191 nJ for the 8 pm, 50 pm 100 pm PCSS devices, respectively. The oscilloscope 505 was triggered by the silicon photodiode 515 that detected scattered light of the laser.

[0076] In various experimental embodiments, the diamond PCSS exhibited a rise time of 4 ns, which is comparable to the rise time of the laser pulse. The minimum PCSS ON- resistances were calculated by applying the voltage divider rule to the 50 Q input resistor:where Rpcss is the minimum PCSS resistance in the ON-state, VDCis the power supply DC voltage, is the peak voltage measured by the oscilloscope 505.Table 4

[0077] Table 4 summarizes the different diamond PCSS devices illustrated in the graphs of FIGs. 12A-12B, with the results obtained at a DC bias of 40 V and 40 pJ and triggered byAttorney Docket No.: 30831.107 (L0103PCT) a 210 nm laser pulse, rj is the quantum efficiency based on the Beer-Lambert law calculated for three devices, e.g., which may be expressed as:where nphotois the photo-excited carrier density, T is the carrier lifetime, I is the laser intensity, R is the reflectance, a is the absorption coefficient, and hat is the photon energy. As can be observed, the B and C diamond PCSS devices performed the best. Peak photocurrent increased significantly from 0.02 A to 0.14 A, as the laser wavelength decreased from 224 nm to 222 nm. This change in peak photocurrent corresponds to the sharp increase in absorption coefficient above the bandgap of diamond.

[0078] The peak photocurrent density of three PCSS devices with electrode spacings of 8 pm, 50 pm, 100 pm at DC power supply voltages from 5 V to 40V is shown in FIG. 13. In all three devices, peak photocurrent density scaled approximately linearly with the applied bias, indicating that velocity saturation was not reached. The PCSS device with 8pm spacing exhibited the highest current density among three devices due to the higher electric field across the illuminated area (50kV / cm) compared to the 50pm and 100pm device.

[0079] In conclusion, the disclosed diamond PCSS devices fabricated on Type Ila diamond showed large ON / OFF ratios, fast risetime and high current densities when excited with an above bandgap laser source. A benchmark of the fabricated diamond PCSS devices compared with previously reported diamond PCSS devices is shown in FIG. 14. The insulating diamond substrate design enables higher photocurrent during the ON-state thanks to the high conductivity p+channel, while no discernable change was observed for the OFF- state.

[0080] FIG. 15 is a flowchart of a method 1500 for manufacturing the diamond PCSS device or system, in accordance with one or more embodiments of the present disclosure. In some embodiments, the method 1500 is performed by semiconductor processing equipment configured to grow insulating diamond substrates and layers, performed disclosed doping, and configured to deposit ohmic contacts in particular location.

[0081] At operation 1510, the processing equipment grows an insulating diamond substrate as a base layer for a power transistor. In various embodiments, the insulating diamond substrate is a Type Ila or Type lb diamond material.

[0082] At operation 1515, the processing equipment optionally grows an insulating diamond layer as a homoepitaxial layer on the insulating diamond substrate.Attorney Docket No.: 30831.107 (L0103PCT)

[0083] At operation 1520, the processing equipment selectively grows a positive p-type diamond layer on the insulating diamond substrate (or insulating diamond layer if operation 1515 is performed) at locations of a set of ohmic contacts.

[0084] At operation 1530, the processing equipment deposits metal electrodes on the positive p-type diamond layer as the set of ohmic contacts.

[0085] In various embodiments, the cleanroom microfabrication process flow of diamond PCSS may utilize similar discrete process steps that led to successful demonstration of world’s highest voltage (e.g., greater than 4.6 kV) diamond Schottky barrier diodes and 222 nm light triggered diamond PCSS. In these embodiments, lateral and vertical diamond PCSS’s can be grown by microwave plasma enhanced chemical vapor deposition (MPCVD).

[0086] In these embodiments, a 200 nm p+ diamond (~ 3 * 1020 cm’3) are selectively grown to form the ohmic contacts. Ohmic metal contacts can be formed by e-beam evaporation of Ti (30 nm) / Pt (30 nm) / Au (100 nm). When and if needed, an AI2O3 field plate is deposited by e-beam evaporation, followed by a lift-off process. AI2O3 was chosen as the field oxide because of its high dielectric constant (k=8.63±0.07 for the as-deposited AI2O3) that reduces the electric field strength and a large band offset for the oxygen- terminated diamond.

[0087] The words “example” or “exemplary” are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example’ or “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words “example” or “exemplary” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims may generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Moreover, use of the term “an implementation” or “one implementation” or “an embodiment” or “one embodiment” or the like throughout is not intended to mean the same implementation or implementation unless described as such. One or more implementations or embodiments described herein may be combined in a particular implementation or embodiment. The terms “first,” “second,” “third,” “fourth,” etc. as usedAttorney Docket No.: 30831.107 (L0103PCT) herein are meant as labels to distinguish among different elements and may not necessarily have an ordinal meaning according to their numerical designation.

[0088] In the foregoing specification, embodiments of the disclosure have been described with reference to specific example embodiments thereof. It will be evident that various modifications can be made thereto without departing from the broader spirit and scope of embodiments of the disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Claims

Attorney Docket No.: 30831.107 (L0103PCT)CLAIMSWhat is claimed is:

1. A system comprising: a power transistor comprising: an insulating diamond substrate that is one of Type Ila or Type lb; and a set of ohmic contacts disposed on or above the insulating diamond substrate to receive current; and a light source configured to inject, into the insulating diamond substrate, an optical signal having a wavelength designed to turn on the power transistor.

2. The system of claim 1, wherein the power transistor further comprises a selectively- grown, positive p-type diamond layer positioned between the insulating diamond substrate and the set of ohmic contacts.

3. The system of claim 1, wherein the set of ohmic contacts comprise a pair of interdigitated electrodes.

4. The system of claim 1, wherein the power transistor is a lateral diamond photoconductive semiconductor switch (PCSS) device, further comprising an insulating diamond layer grown as a homoepitaxial layer on the insulating diamond substrate and being between 0.1% and 20% a thickness of the diamond substrate, wherein the set of ohmic contacts are disposed on the insulating diamond layer.

5. The system of claim 4, wherein the power transistor is to operate in an above-bandgap region of diamond and a wavelength of the optical signal from the light source is shorter than or equal to 224 nanometers (nm).

6. The system of claim 4, wherein the insulating diamond substrate comprises one of a single-crystalline Type Ila or Type lb diamond material that is polished on both sides.

7. The system of claim 1, wherein the power transistor is a vertical diamond PCSS device, wherein the set of ohmic contacts comprise a first ohmic contact disposed on a firstAttorney Docket No.: 30831.107 (L0103PCT) side of the insulating diamond substrate and a second ohmic contact disposed on a second side of the insulating diamond substrate.

8. The system of claim 7, wherein the first ohmic contact comprises a first electrode and the second ohmic contact comprises one of a second electrode opposite the first electrode or a metal plate electrode.

9. The system of claim 7, wherein the power transistor is to operate in an indirect bandgap region of diamond and a wavelength of the optical signal from the light source is shorter than or equal to 224 nm.

10. The system of claim 7, wherein the insulating diamond substrate comprises a Type Ila HPHT diamond material that is polished on both sides.

11. A lateral diamond PCSS device comprising: an insulating diamond substrate that is one of Type Ila or Type lb; an insulating diamond layer grown as a homoepitaxial layer on the insulating diamond substrate and being between 0.1% and 20% a thickness of the insulating diamond substrate; and a pair of interdigitated electrodes disposed on the insulating diamond layer to receive current.

12. The lateral diamond PCSS device of claim 11, wherein a gap is defined between the pair of interdigitated electrodes to enable an optical signal from a light source to pass into the insulating diamond layer and the insulating diamond substrate.

13. The lateral diamond PCSS device of claim 11, further comprising a selectively- grown, positive p-type diamond layer positioned between the insulating diamond layer and the pair of interdigitated electrodes.

14. The lateral diamond PCSS device of claim 11, wherein the insulating diamond substrate comprises one of a single-crystalline Type Ila or Type lb diamond material that is polished on both sides.Attorney Docket No.: 30831.107 (L0103PCT)15. The lateral diamond PCSS device of claim 11, wherein the insulating diamond substrate is between 400 and 600 micrometers in thickness.

16. A vertical diamond PCSS device comprising: an insulating diamond substrate comprising a single-crystalline diamond material that is polished on both sides; a first ohmic contact disposed on a first side of the insulating diamond substrate; a second ohmic contact disposed on a second side of the insulating diamond substrate opposite from the first ohmic contact; and selectively-grown, positive p-type diamond layers positioned between the insulating diamond substrate and each of first and second ohmic contacts.

17. The vertical diamond PCSS device of claim 16, wherein the first ohmic contact comprises a first set of ohmic contacts having a gap therebetween, and the second ohmic contact comprises a second set of ohmic contacts having a corresponding gap therebetween.

18. The vertical diamond PCSS device of claim 17, wherein the first set of ohmic contacts comprises first electrode fingers, wherein gaps between the first electrode fingers are sized to allow a wavelength of an optical signal from a light source of shorter than or equal to 224 nm to pass through a thickness of the insulating diamond substrate.

19. The vertical diamond PCSS device of claim 16, wherein the first ohmic contact comprises a first set of ohmic contacts having a gap therebetween, and the second ohmic contact comprises metal plate electrode.

20. The vertical diamond PCSS device of claim 16, wherein the insulating diamond substrate comprises one of a single-crystalline Type Ila or Type lb diamond material that is polished on both sides, and wherein the insulating diamond substrate is between 200 and 500 micrometers in thickness.

21. A method comprising: growing an insulating diamond substrate as a base layer for a power transistor, wherein the insulating diamond substrate is one of Type Ila or Type lb;Attorney Docket No.: 30831.107 (L0103PCT) selectively growing a positive p-type diamond layer on the insulating diamond substrate at locations of a set of ohmic contacts; and depositing metal electrodes on the positive p-type diamond layer as the set of ohmic contacts.

22. The method of claim 21, further comprising growing an insulating diamond layer as a homoepitaxial layer on the insulating diamond substrate, wherein the positive p-type diamond layer is selectively grown on the insulating diamond layer.

23. The method of claim 22, wherein the insulating diamond layer is between 0.1% and 20% a thickness of the insulating diamond substrate.

24. The method of claim 22, wherein growing the insulating diamond substrate is performed via microwave plasma enhanced chemical vapor deposition (MPCVD).

25. The method of claim 21, further comprising polishing both sides of the insulating diamond substrate.

26. The method of claim 21, wherein the metal electrodes comprise a pair of interdigitated electrodes having a gap therebetween that is sized so that a wavelength of an optical signal from a light source that is shorter than or equal to 224 nm passes through to the insulating diamond substrate.

27. The method of claim 21, wherein depositing the metal electrodes comprises: depositing first electrode fingers on a first side of the insulating diamond substrate; and depositing one of second electrode fingers that correspond to the first electrode fingers or a metal plate electrode on a second side of the insulating diamond substrate.

28. The method of claim 27, wherein the first electrode fingers define a gap therebetween sized so that a wavelength of an optical signal from a light source that is shorter than or equal to 244 nm passes through a thickness of the insulating diamond substrate.

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