Optical depth-sensing system using high-speed colloidal quantum dot photodetectors

Abstract

An optical depth sensing system is provided that includes an active illumination source and a colloidal quantum dot photodetector having colloidal quantum dots as light sensing elements, the system having a rise time of less than 5.0 ns and a fall time of less than 10.0 ns.

Description

Claiming priority

[0001]

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 284,846, entitled "Optical Depth Sensing Systems Using High Speed ​​Colloidal Quantum Dot Photodetectors," filed on December 1, 2021, the contents of which are incorporated by reference into this specification as if set forth in their entirety. [Technical field]

[0002] The present inventive concepts relate generally to photodetectors, and more particularly to colloidal quantum photodetectors and systems including same. [Background technology]

[0003]

[0003] Depth sensing systems that utilize active light sources and optical detectors to determine the distance and three-dimensional structure of objects in a scene and from the system are useful in industrial, scientific, consumer, automotive and security market applications. A significant drawback of conventional approaches to building these systems is the lack of scalable detector structures capable of high-speed detection in the near infrared (NIR) and shortwave infrared (SWIR) spectral regions. Photodetectors commonly used today in the NIR and SWIR spectral bands are typically comprised of silicon (Si)-based photodetectors, germanium (Ge)-based photodetectors, indium gallium arsenide (InGaAs) photodetectors, mercury cadmium telluride (HgCdTe) detectors, and indium antimonide (InSb) detectors. All of these material systems generally suffer from deficiencies, for example, in the noise performance, cost structure or manufacturability of the material system, spectral response range, or some combination of these. Therefore, improved systems are desired. Summary of the Invention

[0004] Some embodiments of the inventive concept provide an optical depth sensing system including an active illumination source and a colloidal quantum dot photodetector having colloidal quantum dots as light sensing elements, the system having a rise time of less than 5.0 ns and a fall time of less than 10.0 ns. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a block diagram illustrating a system used in colloidal quantum dot photodetector response time measurements. [Diagram 2]

[0006] FIG. 2 is an example screenshot of an oscilloscope display when measuring the output of an InGaAs photodiode reference detector and a colloidal quantum dot photodiode while illuminated with the pulsed laser source shown in FIG. 1 in accordance with some embodiments of the inventive concepts. [Diagram 3]

[0007] FIG. 3 is a table illustrating measurement data recorded by the oscilloscope of FIG. 1 reporting average rise / fall times along with additional measurement statistics in accordance with some embodiments of the inventive concepts. [Figure 4A]

[0008] FIG. 4A is a diagram illustrating an example setup used for demonstration of a colloidal quantum dot detector optical depth measurement system according to some embodiments of the inventive concepts. [Figure 4B] FIG. 4B is a diagram illustrating an example setup used for demonstration of a colloidal quantum dot detector optical depth measurement system according to some embodiments of the inventive concepts. [Figure 5A]

[0009] FIG. 5A is an oscilloscope screenshot taken of the electrical output of the colloidal quantum dot and reference detector at position 1 (FIG. 5A) according to some embodiments of the inventive concepts. [Figure 5B]FIG. 5B is an oscilloscope screenshot taken of the electrical output of the colloidal quantum dot and reference detector at position 2 (FIG. 5B) according to some embodiments of the inventive concepts. [Figure 6]

[0010] FIG. 6 is a cross-sectional view illustrating a colloidal quantum dot sensor stack according to some embodiments of the inventive concepts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006]

[0011] The inventive concepts are described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive concepts are shown, however, this inventive concept may be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.

[0007]

[0012] Thus, while the inventive concepts are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are described in detail herein. It is to be understood, however, that there is no intention to limit the inventive concepts to the particular forms disclosed, but rather, the inventive concepts are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the inventive concepts as defined by the claims. Like numbers refer to like elements throughout the description of the figures.

[0008]

[0013] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concepts. As used herein, the singular forms "a," "an," and "the" are intended to include the plural unless the context clearly dictates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including" as used herein specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Furthermore, when an element is referred to as being "responsive to" or "connected" to another element, it may be directly responsive or connected to this other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly responsive to" or "directly connected" to another element, there are no intervening elements present. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as " / ".

[0009]

[0014] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the inventive concept belongs. Furthermore, it will be understood that the terms used herein should be interpreted to have a meaning consistent with the meaning of the terms in the context of the present specification and related technical fields, and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0010]

[0015] It will be understood that terms such as first, second, etc. may be used herein to describe various elements, but these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element can be referred to as a second element, and similarly, a second element can be referred to as a first element, without departing from the teachings of the present disclosure. Some of the drawings include arrows on communication paths to indicate the primary direction of communication, but it will be understood that communication may also occur in the opposite direction to the illustrated arrows.

[0011]

[0016] As used herein, the term "optoelectronic device" generally refers to any device that functions as an optical-electrical or electrical-optical transducer. Thus, the term "optoelectronic device" may refer, for example, to photovoltaic (PV) devices (e.g., solar cells), photodetectors, thermovoltaic cells, or electroluminescent (EL) devices such as light-emitting diodes (LEDs) and laser diodes (LDs). In a general sense, EL devices operate inversely to PV and photodetector devices. Electrons and holes are injected from the respective electrodes into a semiconductor region under the influence of an applied bias voltage. One of the semiconductor layers is chosen for its light-emitting properties rather than its light-absorbing properties. Radiative recombination of the injected electrons and holes produces light emission in this layer. Many of the same types of materials used in PV and photodetector devices can be used in EL devices as well, although the layer thicknesses and other parameters must be adapted to achieve the different goals of the EL device.

[0012]

[0017] As used herein, the term "quantum dot" or "QD" refers to a semiconductor nanocrystal material in which excitons are confined in all three spatial dimensions, and is distinguished from quantum wires (quantum confined in only two dimensions), quantum wells (quantum confined in only one dimension), and bulk semiconductors (unconfined). Many optical, electrical, and chemical properties of quantum dots may also be strongly dependent on the size of the quantum dot, and thus such properties may be modified or tuned by controlling the size of the quantum dot. Quantum dots may generally be characterized as particles, and the shape of a quantum dot may be spheroidal, ellipsoidal, or other shapes. The "size" of a quantum dot may refer to its shape or an approximate dimensional characteristic of its shape, and thus may be the diameter, major axis, dominant length, etc. The size of a quantum dot is on the order of nanometers, i.e., generally in the range of 1.0 to 1000 nm, but more typically in the range of 1.0 to 100 nm, 1.0 to 20 nm, or 1 to 10 nm. In a plurality or collection of quantum dots, the quantum dots may be characterized as having an average size. The size distribution of the plurality of quantum dots may or may not be monodisperse. The quantum dots may have a core-shell configuration, where the core and the surrounding shell may have different compositions. The quantum dots may also include ligands attached to their outer surface or may be functionalized with other chemical moieties for specific purposes.

[0013]

[0018] For purposes of this disclosure, spectral ranges or bands of electromagnetic radiation are generally interpreted as follows, with the understanding that adjacent spectral ranges or bands may be considered to overlap one another to some extent: ultraviolet (UV) radiation may be considered to fall within the range of about 10-400 nm, although in practical applications (above vacuum), the range is about 200-400 nm. Visible light radiation may be considered to fall within the range of about 380-760 nm. Infrared (IR) radiation may be considered to fall within the range of about 750-100,000 nm. IR radiation may also be considered in terms of sub-ranges, examples of which are as follows: short wave infrared (SWIR) radiation may be considered to fall within the range of about 1,000-3,000 nm. mid wave infrared (MWIR) radiation may be considered to fall within the range of about 3,000-5,000 nm. long range infrared (LWIR) radiation may be considered to fall within the range of about 8,000-12,000 nm.

[0014]

[0019] As described below, quantum dot photodiode (QDP) technology is implemented to provide low-cost nanotechnology-enabled photodetectors. In some implementations, the photodetectors can be configured to efficiently detect light with sensitivity across a spectral range of about 250-2400 nm. Thus, the QD photodetectors can be configured as multispectral devices capable of generating images from incident ultraviolet (UV), visible, and / or infrared (IR) electromagnetic radiation. In some implementations, the spectral range of sensitivity can extend down to X-ray energies and / or up to IR wavelengths longer than 2400 nm. The photodetectors taught herein are cost-effective, scalable to large area arrays, and applicable to flexible substrates.

[0015]

[0020] As used herein, "dark current" refers to the residual current that flows through a photoelectric device when there is no incident illumination. In physics and electronics, dark current is a relatively small current that flows through a photosensitive device, such as a photomultiplier tube, photodiode, or charge-coupled device, even when no photons are entering the device. Dark current generally consists of charge that is generated in the detector when no external radiation is entering the detector. This may be called reverse bias leakage current in non-optical devices and is present in all diodes. Physically, on-source dark current is due to the random generation of electrons and holes in the depletion region of the device.

[0016]

[0021] As used herein, the term "fullerene" refers to Buckminsterfullerene C n , and C 70 , C 84 and other forms of molecular carbon such as tungsten, tungsten-based tungsten, and similar cage-like carbon structures, more commonly ranging from 20 to several hundred carbon atoms, i.e., n is 20 or greater. n The fullerenes may be functionalized or chemically modified as desired for a particular purpose, such as to improve solubility or dispersibility, or to modify the electrical properties of the fullerene. The term "fullerene" may also refer to endohedral fullerenes, in which a non-carbon atom or cluster of atoms is encapsulated in a carbon cage. The term "fullerene" may also refer to fullerene derivatives. Some non-limiting examples of fullerene derivatives include [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) and phenyl-C 61 -butyric acid cholestryl ester (PCBCR). The term "fullerene" may also refer to mixtures of the aforementioned forms of fullerene.

[0017]

[0022] As used herein, "pn junction" refers to the interface or boundary between two semiconductor material types, i.e., p-type and n-type, within a semiconductor. In p-type semiconductors, the majority carriers are holes and the minority carriers are electrons. In n-type semiconductors, electrons are the majority carriers and holes are the minority carriers. Semiconductors such as germanium or silicon doped with any of the trivalent atoms such as boron, indium, or gallium can be p-type semiconductors. Phosphorus, arsenic, antimony, bismuth, and the like are used to make n-type semiconductors.

[0018]

[0023] As described above, depth sensing systems that utilize active light sources and optical detectors to determine the distance and three-dimensional structure of objects in a scene and from the system are useful in industrial, scientific, consumer, automotive and security market applications. A significant drawback of conventional approaches to building these systems is the lack of scalable detector structures capable of high-speed detection in the near infrared (NIR) and shortwave infrared (SWIR) spectral regions. Photodetectors commonly used today in the NIR and SWIR spectral bands typically consist of silicon (Si)-based photodetectors, germanium (Ge)-based photodetectors, indium gallium arsenide (InGaAs) photodetectors, mercury cadmium telluride (HgCdTe) detectors, and indium antimonide (InSb) detectors. All of these material systems generally suffer from drawbacks, for example, in the noise performance, cost structure or manufacturability of the material system, spectral response range, or some combination thereof.

[0019]

[0024] Accordingly, some embodiments of the inventive concept provide an optical depth sensing system that includes a high-speed photodetector based on colloidal quantum dots as one or more light-sensing elements. A depth sensing system according to embodiments herein utilizes an active photon source, such as a laser or a light-emitting diode (LED), to generate photons in the NIR or SWIR spectral range.

[0020]

[0025] Although other detector structures have been constructed using colloidal quantum dot materials, none of these detectors have demonstrated the bandwidth and response time required for accurate time-of-flight (ToF) depth sensing. Furthermore, none of the available detector structures have been used in the demonstration of a time optical depth sensing system using direct mode time-of-flight measurements.

[0021]

[0026] As described herein, the colloidal quantum dot photodetector structure is combined with an active illumination source to create an optical depth sensing system. The active illumination source can be, for example, a laser or an LED. The system measures distance based on the measured back reflection of the active light source that is detected by the colloidal quantum dot high speed detector. The system can be operated in several configurations. Exemplary configurations are described below.

[0022]

[0027] As a first example, the system may be operated in a direct time-of-flight configuration that utilizes precise detection and measurement of the amplitude, time, frequency, and related characteristics of reflected light pulses. As used herein, time-of-flight (ToF) refers to a measurement of the round-trip time it takes for a light pulse to travel from a light source to an object and back to a photodetector co-located with the light source. This time information may then be used in conjunction with the speed of light to determine the distance of the object from the ToF system.

[0023]

[0028] As a second example, the system may be operated in an indirect time-of-flight configuration, which relies on measuring and detecting the phase shift of a reflected optical signal as compared to the phase of an emitted optical signal.

[0024]

[0029] Additionally, the system may be operated using measurement and detection of the frequency shift of the reflected optical signal compared to the frequency of the emitted optical signal.

[0025]

[0030] Finally, the system may be operated based on the measurement and detection of an array of emitted optical patterns, such as a grid of laser dots in what is commonly known as a structured light depth sensing system, it being understood that embodiments of the inventive concept are not limited to these examples.

[0026]

[0031] In all of the configurations described above, these depth / distance measurement systems can benefit from the advantages discovered in building systems using high speed colloidal quantum dot photodetectors according to some embodiments of the inventive concepts.

[0027]

[0032] The colloidal quantum dot photodiode structures described herein are capable of providing sufficient bandwidth, response time, thermal operating limits, manufacturability, and cost scalability typically required for optical depth sensing solutions in industrial, consumer, and automotive systems.

[0028]

[0033] The colloidal quantum dot photodiode structure described herein has distinct properties that give it technical and commercial advantages over previous work. For example, these properties include the design and fabrication of a pn photodiode structure that operates with diffusion dominated charge transport properties. For example, the photodiode structure can be designed and constructed to have a small depletion region, e.g., less than 50 nm thick, with a diffusion transport region that is 50 nm to 250 nm in length.

[0029]

[0034] Additionally, the photodiode structure can be operated at low bias voltages, e.g., 0 mV to 1000 mV applied bias. This low operating bias results in superior temporal response and dark noise performance compared to other approaches for constructing colloidal quantum dot photodetectors. Specifically, the system exhibits rise times of less than 5.0 ns and fall times of less than 10.0 ns. As used herein, "rise time" refers to the length of time it takes a signal to rise from 10% to 90% of its full-scale value. Similarly, as used herein, "fall time" refers to the length of time it takes a signal to fall from 90% to 10% of its full-scale value.

[0030]

[0035] The dark current characteristics of the colloidal quantum dot photodiodes described herein are also superior to conventional devices. Low dark current is advantageous for optical depth sensing systems, since dark current strongly contributes to the amount of background noise present in the system. As a result, dark current strongly influences the design and performance of the sensing system. For example, the dark current of the detector can impose requirements on the light source in the system to generate sufficient optical power to overcome the dark noise of the detector. The colloidal quantum dot photodiodes demonstrated here have a dark current of 50 nA / cm at 25°C. 2 The dark currents are measured at the same applied bias voltage at which the detector is operated during the light detection operation. In other words, the externally applied bias voltage during the light detection operation is the same value as the externally applied bias voltage used during the dark signal measurement.

[0031]

[0036] In some embodiments, the colloidal quantum dot fast photodiode detector structure is designed as a photovoltaic junction, where the extraction of photo-generated charge carriers to an external circuit does not require the application of a bias voltage. This is because the internally generated electric field and charge carrier diffusion gradient are sufficient for the extraction of photo-generated charges. This colloidal quantum dot-based photovoltaic pn junction has the advantage of avoiding the very long signal transients, i.e., signal decay times, typically found in other types of colloidal quantum dot photodetectors. This is one of the main contributing factors to the extremely fast photoresponse times measured in this depth sensing system.

[0032]

[0037] Referring now to FIG. 1, a block diagram illustrates a system using a colloidal quantum dot photodetector in an optical depth sensing system. As illustrated in FIG. 1, the system includes an active illumination source 105, a reference detector 115, a high-speed photodetector 120 including colloidal quantum dots, and an oscilloscope 125. The active illumination source 105 can be, for example, a laser or an LED. In FIG. 1, the active illumination source is a Nd:YAG (Neodymium doped Yttrium Aluminum Garnet) pulsed laser. As illustrated, the Nd:YAG laser generates a laser output 110, for example, the Nd:YAG laser emits a series of laser pulses that travel through air and illuminate the colloidal quantum dot photodiode detector 120 and an InGaAs photodiode used as the reference detector 115 in the embodiment illustrated in FIG. 1. In the illustrated embodiment, the Nd:YAG laser 105 is configured to operate at a wavelength of 1064 nm with a full width at half maximum pulse width of 3.0-5.0 ns, a repetition rate of 5 Hz. The colloidal quantum dot photodiode is a 0.2 mm x 0.2 mm square detector, the electrical output of which is connected to an oscilloscope 125, e.g., Agilent part number MSO8104A, as shown. The InGaAs reference photodiode 115 is a 0.15 mm diameter detector, e.g., Thorlabs part number FGA015, the electrical output of which is also connected to an oscilloscope 125, as shown, for use as a trigger source for the oscilloscope measurements.

[0033]

[0038] The colloidal quantum dot photodiode 120 can be, but is not limited to, a photodiode from SWIR Visions systems, e.g., 200 μm×200 μm. Furthermore, the connector between the devices can be a coaxial cable without departing from the scope of the inventive concept.

[0034]

[0039] The system 100 of Figure 1 is provided to demonstrate the functionality of a colloidal quantum dot detector-based optical depth sensor system according to some embodiments of the inventive concepts. As shown, a colloidal quantum dot photodiode 120 was used to measure the rise and fall time characteristics of a laser pulse 110. Data collected from the system of Figure 1 will now be described with respect to Figures 2 and 3.

[0035]

[0040] In particular, FIG. 2 is a screenshot of an oscilloscope display illustrating the output of an InGaAs photodiode reference detector and a colloidal quantum dot photodiode, according to an embodiment described herein. During this measurement, the oscilloscope was configured to measure the 10% to 90% rise time and the 90% to 10% fall time for the reference detector and the colloidal quantum dot detector. The average rise / fall times are illustrated in FIG. 3 along with additional measurement statistics. This measurement data was reported by the oscilloscope. The colloidal quantum dot detector shows an average rise time of 1.01 ns and an average fall time of 2.79 ns. Both the rise and fall times were shorter than those measured using the InGaAs reference detector. Measurement of rise and fall times of less than 5 ns using the colloidal quantum dot detector illustrates that an embodiment of the inventive concept has the time response characteristics required for a depth sensing system.

[0036]

[0041] To demonstrate the colloidal quantum dot detector optical depth measurement system according to some embodiments of the inventive concepts, an example system is illustrated in Figures 4A and 4B. As illustrated, the system includes an active illumination source 405, e.g., a laser or LED, a reference detector 415, and a colloidal quantum dot detector 420. The system is used to illuminate a piece of white plastic 430. In this two-part measurement, a laser pulse (transmitted laser pulse in Figure 4A) was used to illuminate the piece of white opaque plastic 430. The laser pulse is then reflected from the plastic 430 (reflected laser pulse in Figure 4A) and the reflected light is detected by both the reference detector 415 and the colloidal quantum dot detector 420. The electrical output of both detectors 415 and 420 was measured by an oscilloscope (not shown - see 125 in Figure 1). The detectors 415 and 420 and the oscilloscope 125 used in this measurement were similar to those described with respect to Figure 1.

[0037]

[0042] As illustrated in Figure 4A, in the first part of the measurement, the reference detector 415 and the colloidal quantum dot detector 420 were placed in the same location and at the same distance from the reflective white plastic surface 420. As illustrated in Figure 4B, in the second part of this measurement, the colloidal quantum dot detector 420 was moved 28 cm away from the reference detector position 415. This resulted in a 28 cm path length difference that the light pulse (the reflected laser pulse) had to travel before being detected by the colloidal quantum dot detector 420.

[0038]

[0043] Figures 5A and 5B are screenshots taken of the electrical output of the colloidal quantum dot and reference detectors at position 1 (Figure 4A) and position 2 (Figure 4B). At position 1 (Figure 4A), the detectors are co-located. At position 2, the detectors are 28 cm apart. The time difference between the 50% signal levels at the rising edge of the two detector outputs was measured using an oscilloscope for both detector positions. The change in arrival time difference between the two measurements was 0.94 ns. This 0.94 ns shift in pulse arrival time was caused by an increase of 28 cm in the distance that the light pulse had to travel through free space between the two measurements.

[0039]

[0044] The following equation represents a calculation to estimate the change in optical path length resulting from the 0.94 ns change in pulse arrival time measured in FIGS. 5A and 5B: d=ct formula (1) where d is the change in distance, c is the speed of light, and t is the change in time. Putting in the values: d=2.997E8m / s*0.94E-9s d=0.282m d=28.2cm Therefore, using the speed of light in air, it can be calculated that in 0.94 ns, the light pulse is expected to travel 28.2 cm. This agrees well with the measured change in optical path length of 28 cm. These measurements therefore illustrate that an optical depth sensing system with colloidal quantum dot detectors can be implemented to measure distance in time-of-flight three-dimensional (3D) depth sensing.

[0040]

[0045] 6, an exemplary colloidal quantum dot sensor stack that may be used in accordance with some embodiments of the inventive concepts is described. The colloidal quantum dot sensor stack 600 includes a silicon readout integrated circuit 640 with metal pixel electronics 650. A colloidal quantum dot photodiode 660 is provided on the electronics 650, and an encapsulant 670 is provided on the photodiode 660. Exemplary structures are provided in commonly assigned U.S. Patent Application Publication Nos. 2021 / 0288195 and 2022 / 0231244, the contents of which are incorporated by reference herein as if set forth in their entirety. The colloidal quantum dot photodetector may be any colloidal quantum dot photodetector without departing from the scope of the inventive concepts.

[0041]

[0046] Accordingly, some embodiments of the inventive concepts provide photodetector structures constructed for depth sensing that are fabricated using colloidal quantum dot optical absorbers; operate without active cooling; exhibit 10%-90% rise / fall times shorter than 10 ns; have a bandwidth (BW) greater than 100 MHz; operate in response to light having a wavelength in the range of 900 nm to 2500 nm; may be single elements, linear arrays, or two-dimensional arrays of detectors to enable high frame rates, high resolution sensing, and solid-state systems without the need for scanning or rotation or other mechanical motion; fabricated using a p-n junction formed between two adjacent colloidal quantum dot layers, or between a colloidal quantum dot layer and a fullerene layer; fabricated using a p-n junction formed using at least one colloidal quantum dot material, where the charge transport properties are dominated by diffusion processes and incorporate a depletion width smaller than 50 nm.

[0042]

[0047] As briefly described above, some embodiments of the inventive concept provide high speed colloidal quantum dot photodiode structures that can be used as photosensing elements for optical depth sensing, ranging, gesture recognition, face mapping, LIDAR, and / or other three-dimensional (3D) depth sensing systems.

[0043]

[0048] In the drawings and specification, illustrative embodiments of the inventive concepts are disclosed. However, many variations and modifications can be made to these embodiments without substantially departing from the principles of the inventive concepts. Thus, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive concepts being defined by the following claims.

Claims

1. 1. An optical depth sensing system, comprising: an active illumination source; a colloidal quantum dot photodetector configured to receive light from the active illumination source, wherein the colloidal quantum dot photodetector has colloidal quantum dots as light-sensing elements; Equipped with An optical depth sensing system, wherein the signal output from the colloidal quantum dot photodetector has a rise time of less than 5.0 ns and a fall time of less than 10.0 ns.

2. The system of claim 1 , wherein the active illumination source is one of a laser or a light emitting diode (LED).

3. The system of claim 1 , wherein the system measures distance based on a measured back reflection of the active illumination source detected by the colloidal quantum dot photodetector.

4. The system of claim 1 , wherein the active illumination source generates photons in the near-infrared (NIR) or short-wave infrared (SWIR) spectral region.

5. 10. The system of claim 1, wherein the system is operated at a low bias voltage, the low bias voltage being between 0 mV and 1000 mV of applied reverse bias.

6. The system of claim 1 , wherein the system operates without active cooling.

7. The system of claim 1 , wherein the system exhibits 10% to 90% rise / fall times of less than 10 ns.

8. The system of claim 1 , wherein the system exhibits a bandwidth greater than 100 MHz.

9. 10. The system of claim 1, wherein the system operates in response to light having a wavelength in the range of 900 nm to 2500 nm.

10. 10. The system of claim 1, wherein the colloidal quantum dot photodetector comprises a single element, a linear array, or a two-dimensional array of detectors to enable high frame rate, high resolution sensing, and a solid-state system.

11. 10. The system of claim 1, wherein the system comprises a pn junction formed between two adjacent colloidal quantum dot layers or a pn junction formed between a colloidal quantum dot layer and a fullerene layer.

12. The system of claim 11 , wherein the pn junction comprises at least one colloidal quantum dot material.

13. The system of claim 1 , wherein the charge transport properties of the system are dominated by diffusion processes and incorporate a depletion width of less than 50 nm.

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