Method for evaluating photoelectric characteristics of internal functional area of semiconductor material or device

Abstract

The invention discloses a method for evaluating photoelectric characteristics of a functional area in a semiconductor material or device. The method comprises the following steps: A, pre-processing a semiconductor material or a device to form a cross section which passes through a functional area to be evaluated and has nanoscale flatness, and preparing a common electrode which is in ohmic contact with the semiconductor material; b, measuring the electrical distribution of the functional area in the to-be-tested sample by using an electrical measurement mode of a scanning probe microscope under the condition of no illumination; c, selecting a light source with a proper wavelength to irradiate the semiconductor material or device, and measuring the electrical distribution of the internal functional area of the to-be-tested sample under the illumination condition; and D, comparing, processing and analyzing the measured electrical distribution under the conditions of no illumination and illumination. The method has nanoscale spatial resolution and high sensitivity, can directly obtain the photoelectric characteristics of semiconductor materials and core functional areas in devices, is used for accurately positioning parts influencing the performance of the semiconductor materials and the devices, and quantifies the local photoelectric characteristics, thereby guiding the analysis, prediction and optimization of the performance of the semiconductor materials and the devices.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the photoelectric characteristics of a semiconductor material or an internal functional area of ​​a device, and in particular to a method for evaluating the characteristics such as carrier distribution of a semiconductor material or an internal functional area of ​​a device under light excitation conditions. Background Art

[0002] Semiconductor materials and devices play an extremely important role in modern electronic and optoelectronic technologies. Their electrical or optoelectronic performance is mainly determined by the internal functional regions. The functional regions of semiconductor optoelectronic materials and devices include the active region of light-emitting and laser devices, the absorption region, junction region, and multiplication region of detection devices. In these functional regions, carriers (electrons and holes) transition between different energy states under the action of electric field drive or light excitation, corresponding to the emission and absorption of photons, thereby realizing energy conversion or information transmission between electricity and light. Therefore, the optoelectronic process of the functional region, such as the change in carrier concentration caused by light excitation and its microscopic distribution, dominates the performance of semiconductor materials or devices.

[0003] At present, the main methods for measuring and evaluating the optoelectronic properties of semiconductor materials and devices are laser beam induced photocurrent method (LBIC) and scanning photocurrent imaging method (SPCM). Both methods use a focused light beam to scan and irradiate the surface or functional area of ​​the semiconductor material device to read the electrical response of the device. The advantages are non-destructive measurement and spatial resolution and imaging capabilities. The shortcomings of this type of method are that the measurement obtains the overall optoelectronic response of the device under micro-area excitation, rather than directly extracting the local optoelectronic response, which is not conducive to excluding the influence of other areas on the photocurrent; second, the resolution is determined by the size of the spot, which is generally hundreds of nanometers or more, while many functional layers of semiconductor optoelectronic devices are only tens or even a few nanometers thick; third, the measurement of this type of method is usually an optical scan in the plane, which makes it difficult to extract the optoelectronic characteristics of the device in the depth direction, and is not conducive to analyzing most optoelectronic materials and devices with longitudinal structures. In addition, there are also some technologies that can measure the carrier concentration distribution inside semiconductor materials, such as electrochemical capacitance voltage (ECV), which can achieve a resolution of nanometers. However, the carrier distribution in the material is obtained under light-free conditions, which cannot directly reflect the local photoelectric properties. Moreover, this type of method is difficult to effectively analyze devices or materials with complex functional structures.

[0004] The scanning capacitance microscopy technology among scanning probe technologies has the high spatial resolution of the carrier layout state as its main feature; it can provide information on the lateral diffusion depth, draw a two-dimensional distribution image of the carriers, and can also display the changes in the concentration and polarity of photogenerated carriers in the region under the condition of an external laser. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the photoelectric properties of the internal functional area of ​​a semiconductor material or device, mainly to solve the defects existing in the above-mentioned prior art. The method utilizes light excitation means, combined with local differential capacitance measurement under no light conditions, and obtains the photoelectric information of the internal functional layer by performing difference or differential processing on the measurement results.

[0006] To achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0007] A method for evaluating the photoelectric properties of a semiconductor material or an internal functional area of ​​a device, characterized in that the steps are as follows:

[0008] A. Pre-processing the semiconductor material or device, i.e., the sample to be tested, to form a cross section passing through the functional area to be evaluated, and the cross section has nanometer-level flatness, and preparing a common electrode that forms an ohmic contact with the semiconductor material;

[0009] B. Under the condition of no light, use the electrical measurement mode of the scanning probe microscope to measure the electrical distribution of the internal functional area of ​​the test sample;

[0010] C. Select a light source with a suitable wavelength to illuminate the semiconductor material or device, and measure the electrical distribution of the internal functional area of ​​the test sample under illumination conditions;

[0011] D. Compare, process and analyze the electrical distributions obtained under no-light and light conditions.

[0012] The method for evaluating the photoelectric properties of the internal functional area of ​​a semiconductor material or device is characterized in that: measuring the electrical distribution of the test sample in steps A and B includes using a scanning probe microscope, wherein the electrical measurement mode includes a conductive atomic force microscopy mode or a scanning capacitance microscopy mode.

[0013] The method for evaluating the photoelectric properties of the internal functional area of ​​a semiconductor material or device is characterized in that: the no-light measurement condition described in step B requires moving the light spot on the probe cantilever beam in the scanning probe microscope to a distance of at least 90 microns from the front end of the needle tip to ensure that the functional area of ​​the semiconductor material or device is not excited by the light spot.

[0014] The method for evaluating the photoelectric properties of the internal functional area of ​​a semiconductor material or device is characterized by: the light source of appropriate wavelength is selected to irradiate the semiconductor material or device as described in step C, wherein the wavelength of the light source is selected so that the energy of the irradiated photons is greater than the bandgap width of the semiconductor material in the functional area to be measured, and light sources of different wavelengths are selected for the functional areas of different semiconductor materials to irradiate the samples respectively, and step C is repeated for measurement.

[0015] The method for evaluating the photoelectric properties of the functional area inside the semiconductor material or device is characterized in that: the comparison, processing and analysis of the electrical distribution results obtained by measurement in step D includes difference processing of the electrical distribution under the conditions of light and without light conditions to obtain the net photoelectric signal distribution of the functional area, which is a reflection of the photoelectric efficiency of the functional area of ​​the semiconductor material or device at the nanoscale; or further numerically differentiating the relative position of the photoelectric signal distribution of the functional area to obtain the gradient information of the photoelectric characteristics inside the semiconductor material device, which reflects the effectiveness of the built-in electric field of the functional area acting on photogenerated carriers (electrons and holes).

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The method of the present invention has nanometer-level spatial resolution and can measure and evaluate semiconductor materials and devices containing micro-nano functional layers or complex structures.

[0018] 2. The method of the present invention has high sensitivity, and carrier distribution measurement can be achieved under low light intensity conditions.

[0019] 3. The method of the present invention can perform difference calculation and differential calculation on the carrier distribution information to obtain the minority carrier distribution information and the gradient distribution information of the photogenerated carriers inside the semiconductor material or device.

[0020] 4. The method of the present invention is easy to implement, has high measurement reliability, and the detection is non-destructive and can be repeated. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of a detection system using the method of the present invention.

[0022] Figure 2 Schematic diagram of the detection system and detection method of Example 1 of the present invention; wherein 101 is a substrate; 102 is a multiplication layer; 103 is a buffer layer; 104 is an absorption layer; 105 is a gradient layer; 106 is a charge layer; 107 is a scanning capacitance microscopy measurement circuit; 108 is a diffusion layer; 109 is a probe cantilever; and 110 is a growth direction.

[0023] Figure 3 1 is a differential capacitance distribution diagram of the InGaAS / InP SPAD cross section along the growth direction in Example 1 of the present invention under the conditions of no illumination and light excitation at a wavelength of 1060 nm.

[0024] Figure 4 1 is a differential capacitance distribution diagram of the InGaAS / InP SPAD cross section along the growth direction in Example 1 of the present invention under the conditions of no illumination and light excitation at a wavelength of 830 nm.

[0025] Figure 5This is a distribution diagram of the minority carrier differential capacitance under 1060nm light excitation conditions in Example 1 of the present invention.

[0026] Figure 6 Example 1 of the present invention is a gradient distribution diagram of photogenerated carriers under 1060nm light excitation conditions. DETAILED DESCRIPTION

[0027] See also Figure 1 The present invention discloses a method for evaluating the photoelectric properties of a semiconductor material or a functional area inside a device, in particular, a method for evaluating the characteristics of a semiconductor material or a functional area inside a device under light excitation conditions, such as carrier distribution. The steps of the method are as follows:

[0028] A. Pre-treat the sample to be tested, and prepare the dielectric layer and common electrode. The first is pre-treatment, so that the cross section of the semiconductor material or device forms a nano-level flat surface, which can be prepared by dissociation along a specific crystal direction, or by polishing after cutting. Secondly, the surface or sidewall of the sample to be tested is prepared to form a flat surface covered with a thin dielectric layer; for Group IV semiconductors, it can be prepared by surface oxidation in an ultraviolet irradiation ozone environment; for Group III-V and other compound semiconductors, it can be prepared by the natural oxide layer of the cross section. Finally, the common electrode preparation can be connected to the sample to be tested by evaporation or coating of an appropriate metal layer to form an ohmic contact.

[0029] B. Measure the electrical distribution of the internal functional area of ​​the semiconductor material or device under no light conditions. This step includes using scanning capacitance microscopy (SCM) to measure the carrier distribution information of the internal functional area of ​​the sample to be tested. It is necessary to move the light spot on the cantilever beam of the probe in the scanning probe microscope to at least 90 microns away from the front end of the needle tip to ensure that the functional area of ​​the semiconductor material or device is not excited by the light spot.

[0030] C. Under light excitation conditions, measure the electrical distribution of the semiconductor material or the internal functional area of ​​the device. This step requires the selection of a light source with a photon energy greater than the bandgap width of the semiconductor material in the area to be measured based on the measurement under no light conditions, and the adjustment of the light excitation intensity to irradiate the sample to be tested. It is necessary to ensure that the light source has a stable input to obtain reliable and repeatable measurement results. Different wavelengths of light sources can be selected for irradiation of functional areas of different semiconductor materials.

[0031] D. Compare, process and analyze the electrical distribution results measured under no-light and light-excitation conditions, including difference calculation and differential calculation, so as to obtain the net photoelectric signal distribution and the gradient information of the photoelectric characteristics of the internal functional area of ​​the semiconductor material or device.

[0032] The following is a detailed description of the present invention using the acquisition of the spatial distribution of carriers of an InGaAs / InP single photon avalanche diode (SPAD) as an example and in conjunction with the accompanying drawings, but the present invention is by no means limited to this example.

[0033] Figure 2 Schematic diagram of the detection system and detection method of Example 1 of the present invention. The sample to be tested includes a substrate 101, a buffer layer 103, an absorption layer 104, a gradient layer 105, a charge layer 106, a multiplication layer 102, and a diffusion layer 108 according to the growth direction 110; the absorption layer 104 is non-doped i-InGaAs; the gradient layer 105 is non-doped i-InGaAsP; the charge layer 106 is n - -InP; the multiplication layer 102 is i-InP, and the diffusion layer 108 is p + -InP; the gradient layer is only tens of nanometers, and the charge layer and multiplication layer are both sub-micron level.

[0034] The sample preparation includes two steps: sample pretreatment and common electrode preparation. A nanometer-level flat test surface is prepared for the test sample, and the root mean square roughness of the test surface is required to be no more than 0.2 nanometers. For the InGaAs / InP single-photon avalanche diode (SPAD) in the embodiment, mechanical dissociation along the

[110] crystal direction through the Zn diffusion region can obtain an atomically flat test section. After successful cleavage, the test section of the sample is placed vertically upward, and the bottom is glued to the iron sheet with conductive silver glue to form a common electrode at the same time. In this embodiment, the natural oxide layer of the InGaAs / InP SPAD is directly used as the dielectric layer.

[0035] Using a Pt-coated Si probe, the light spot in the scanning capacitance microscope system is irradiated on the probe cantilever 109 90 um away from the front section of the needle tip. The differential capacitance of the test area is measured using the scanning capacitance microscope under no light conditions. The AC bias voltage is 1 V. The two-dimensional differential capacitance data of the carrier distribution characteristics of the device test area are recorded through the loop 107. Figure 3 and Figure 4 Differential capacitance curve under no light conditions.

[0036] With the help of an infrared viewer, the light spot is irradiated onto the sample. For the absorption region i-InGaAs, the photon energy hv of the excitation light used must be able to excite the interband transition of the InGaAs absorption layer and be lower than the InP band gap. The laser wavelength selected in this embodiment is 1060nm. By quantitatively changing the laser incident power density and thus changing the illumination intensity, the carrier distribution information of the device is obtained by measuring with a scanning capacitance microscope, see Figure 3 The figure shows that at 0.07mW / cm 2Under the light intensity conditions, the dC / dV signal in the absorption area changed from negative (-235.4mV) to positive (19.3mV).

[0037] The same as the above steps, the test is carried out under the conditions of no light and light excitation, except that for the multiplication region i-InP, the excitation light photon energy hv used needs to be able to excite the interband transition of the InP multiplication layer. The laser wavelength selected in this embodiment is 830nm, see Figure 4 The figure shows that at 0.07mW / cm 2 Under the light intensity condition, the dC / dV signal in the multiplication zone also changes from -304.5mV to -158.8mV (the lowest value in the multiplication zone).

[0038] The electrical distribution results obtained by measurement are compared, processed and analyzed. Figure 3 The data measured at 1060nm is the original data. First, the difference between the measurement results under illumination and the measurement results without illumination is processed to obtain the differential capacitance distribution of minority carriers. It is obvious that the net photoelectric signal is very strong in the absorption region. Figure 5 Secondly, the measurement results under illumination are differentiated in the growth direction to obtain the gradient distribution of photogenerated carriers in the device. The gradient extreme value positions similar to positions 1 and 2 in the figure correspond to the extreme values ​​of the field strength inside the device. In addition, in this embodiment, the gradient layer and the charge layer can be clearly identified under 1060nm illumination conditions. Figure 6 . Figure 4 The electrical distribution results obtained by measurement can also be compared, processed and analyzed, which will not be elaborated here.

Claims

1. A method for evaluating the photoelectric properties of a semiconductor material or an internal functional area of ​​a device, characterized in that: It follows these steps: A. Pre-processing the semiconductor material or device, i.e., the sample to be tested, to form a cross section passing through the functional area to be evaluated, and the cross section has nanometer-level flatness, and preparing a common electrode that forms an ohmic contact with the semiconductor material; B. Under the condition of no light, use the electrical measurement mode of the scanning probe microscope to measure the electrical distribution of the internal functional area of ​​the test sample; C. Select a light source with a suitable wavelength to illuminate the semiconductor material or device, and measure the electrical distribution of the internal functional area of ​​the test sample under illumination conditions; D. Compare, process and analyze the electrical distributions obtained under no-light and light conditions.

2. The method for evaluating the photoelectric properties of the internal functional area of ​​a semiconductor material or device according to claim 1, characterized in that: Measuring the electrical distribution of the sample to be tested in steps A and B includes using a scanning probe microscope, wherein the electrical measurement mode includes a conductive atomic force microscopy mode or a scanning capacitance microscopy mode.

3. The method for evaluating the photoelectric properties of a semiconductor material or an internal functional area of ​​a device according to claim 1, characterized in that: The no-light measurement condition described in step B requires moving the light spot on the probe cantilever in the scanning probe microscope to a distance of at least 90 microns from the front end of the needle tip to ensure that the functional area of ​​the semiconductor material or device is not excited by the light spot.

4. The method for evaluating the photoelectric properties of a semiconductor material or an internal functional area of ​​a device according to claim 1, characterized in that: The step C describes selecting a light source of appropriate wavelength to illuminate the semiconductor material or device, wherein the wavelength of the light source is selected so that the energy of the irradiated photons is greater than the bandgap width of the semiconductor material in the functional area to be measured. For functional areas of different semiconductor materials, light sources of different wavelengths are selected to illuminate the samples respectively, and step C is repeated for measurement.

5. The method for evaluating the photoelectric properties of a semiconductor material or an internal functional area of ​​a device according to claim 1, characterized in that: The comparison, processing and analysis of the electrical distribution results obtained by measurement in step D include differential processing of the electrical distribution under conditions of illumination and non-illumination to obtain the net photoelectric signal distribution of the functional area, which is a reflection of the photoelectric efficiency of the semiconductor material or device functional area at the nanoscale; or further numerical differentiation of the relative position of the photoelectric signal distribution of the functional area to obtain the gradient information of the photoelectric characteristics inside the semiconductor material device, which reflects the effectiveness of the built-in electric field of the functional area on the photogenerated carriers.

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