Haoyang Cui

Extraction of Schottky barrier height in Hg0.702Cd0.298Te photovoltaic infrared detector pixel arrays by transient photovoltage measurements

A novel method for extracting the Schottky barrier height (SBH) of a pn-junction-type HgCdTe photodetector by photovoltage measurement has been proposed. The photovoltages of the pn junction and Schottky junction are saturated by the bias light and transient laser pulses. The SBH is obtained as 0.228 eV, which is basically in agreement with the value obtained by the current–voltage technique. Because of the absence of complication due to the interference of the pn junction in the photovoltage measurement, this method is suitable for extracting the low SBH of the pn-junction-type photodiode, whose rectifying behavior of the Schottky contact is unclear.

The methods in infrared thermal imaging diagnosis technology of power equipment

Infrared thermography, which has been widely used, is an important electrical equipment monitoring and fault diagnosis technology. It has two key steps about infrared thermal image processing and artificial intelligence diagnosis faults. In order to improve the accuracy of diagnosing electrical equipment thermal fault, the algorithms of denoising, segmentation and feature extraction in image processing, the BP and RBF network model of neural networks for intelligent diagnosis are discussed with the specific experimental conditions, the advantages and disadvantages of the various technologies and the improved methods are pointed out.

Experimental determination of minority carrier lifetime and recombination mechanisms in MCT photovoltaic detectors

This paper presents an experimental study of minority carrier lifetime and recombination mechanisms in HgCdTe photodiode. The excitation light source is a wavelength-tunable pulsed infrared laser. A constant background illumination has been introduced to minimize the effect of the junction equivalent capacitor and the equivalent series resistance. The slow decay of the photo-generated voltage is recorded by a storage oscilloscope. By fitting the exponentially decay curve, the time constant has been obtained which is regarded as the photo-generated minority carrier lifetime of the HgCdTe photodiode. The experimental results show that the carrier lifetime is in the range of 18 ~ 407 ns at 77 K for the measured detectors of four compositions. It was found that the Auger recombination process is more effective for low Cd composition while the radiative recombination process became more important for high compensated materials. The Shockley-Read-Hall (SRH) recombination processes could not be ignored for all Cd composition.

Analysis of temperature distribution characteristics from an improved IGBT power cycling test

The power cycling test is an important method to study the reliability of IGBT module. In order to solve the problem that traditional power cycling test simulation load is too idealistically, we proposed an improved power cycling test simulation based on the traditional power cycling test simulation considering the anode spike voltage during turn off process and the voltage drop of MOSFET and PNP transistors device in the process of conducting. In addition, using ANSYS simulation software for simulate the both power cycling test, we get the temperature field distribution of the IGBT module by the two power cycling simulation. Considering the transient characteristics during the IGBT turn-off process, so that the loads in improved power cycling test simulation more realistic, therefore a more accurate simulation result than traditional test. Nearly 10% lower than the highest temperature of the temperature field of conventional power cycling test. This simulation provides a more accurate theory for the power cycling test in the IGBT applications.

Dependence of Cd compositione on transient photovoltage characteristics in Hg 1−x Cd x Te photodiode

This paper presents an experimental study of transient photovoltage induced by the pulsed laser excitation in the HgCdTe pn junction photodiode. The excitation light source is a wavelength-tunable pulsed infrared laser. The photo-response shows an apparent negative valley during the first then evolves into a positive peak. An obviously magnitude decreasing of the negative valley can be observed as the Cd composition decrease. When the experiment temperature increase from liquid nitrogen to room temperature, only the positive peak can be observed even the photodiode illuminated by the strong laser intensity. This shows that the negative valley of the transient photovoltage can be attributed to the Schottky barrier at metal-semiconductor (M/S) interface, and the M/S interface photovoltaic effect influenced by the Cd composition and the temperature.

Experimental Determination of Effective Minority Carrier Lifetime in HgCdTe Photovoltaic Detectors Using Optical and Electrical Methods

This paper presents experiment measurements of minority carrier lifetime using three different methods including modified open-circuit voltage decay (PIOCVD) method, small parallel resistance (SPR) method, and pulse recovery technique (PRT) on pn junction photodiode of the HgCdTe photodetector array. The measurements are done at the temperature of operation near 77 K. A saturation constant background light and a small resistance paralleled with the photodiode are used to minimize the influence of the effect of junction capacitance and resistance on the minority carrier lifetime extraction in the PIOCVD and SPR measurements, respectively. The minority carrier lifetime obtained using the two methods is distributed from 18 to 407 ns and from 0.7 to 110 ns for the different Cd compositions. The minority carrier lifetime extracted from the traditional PRT measurement is found in the range of 4 to 20 ns for . From the results, it can be concluded that the minority carrier lifetime becomes longer with the increase of Cd composition and the pixels dimensional area.

Determination of minority carrier lifetime in mercury-cadmium telluride photovoltaic detectors using parallel resistance method

This paper presents a minority carrier lifetime extraction method using transient photovoltage method. The excitation light source is a picosecond pulsed infrared laser. A parallel resistance has been introduced to minimize the effect of the equivalent junction series resistance effect. A storage oscilloscope has been used to record the photovoltage of the photodiode. By fitting the exponentially decay curve, the time constant has been obtained which is regarded as the photo-generated minority carrier lifetime of the photodiode. The experimental results show that the carrier lifetime is in the range of 0.7~110 ns at 77 K for the measured detectors of four compositions. The results indicate that the lifetime become longer with the increase of Cd composition.

The Effect of Metal-Semiconductor Contact on the Transient Photovoltaic Characteristic of HgCdTe PV Detector

The transient photovoltaic (PV) characteristic of HgCdTe PV array is studied using an ultrafast laser. The photoresponse shows an apparent negative valley first, then it evolves into a positive peak. By employing a combined theoretical model of pn junction and Schottky potential, this photo-response polarity changing curves can be interpreted well. An obvious decreasing of ratio of negative valley to positive peak can be realized by limiting the illumination area of the array electrode. This shows that the photoelectric effect of Schottky barrier at metal-semiconductor (M/S) interface is suppressed, which will verify the correctness of the model. The characteristic parameters of transient photo-response induced from p-n junction and Schottky potential are extracted by fitting the response curve utilizing this model. It shows that the negative PV response induced by the Schottky barrier decreases the positive photovoltage generated by the pn junction.

Optical Limiting Using the Two-Photon Absorption Electrical Modulation Effect in HgCdTe Photodiode

The electrical modulation properties of the output intensity of two-photon absorption (TPA) pumping were analyzed in this paper. The frequency dispersion dependence of TPA and the electric field dependence of TPA were calculated using Wherrett theory model and Garcia theory model, respectively. Both predicted a dramatic variation of TPA coefficient which was attributed into the increasing of the transition rate. The output intensity of the laser pulse propagation in the pn junction device was calculated by using function-transfer method. It shows that the output intensity increases nonlinearly with increasing intensity of incident light and eventually reaches saturation. The output saturation intensity depends on the electric field strength; the greater the electric field, the smaller the output intensity. Consequently, the clamped saturation intensity can be controlled by the electric field. The prior advantage of electrical modulation is that the TPA can be varied extremely continuously, thus adjusting the output intensity in a wide range. This large change provides a manipulate method to control steady output intensity of TPA by adjusting electric field.

The Simulation and Analysis of Temperature Field Distribution of Core in Dry-Type Power Transformer

The temperature elevate of transformer core is one of the most important parameter must be considered in the transformers design and manufacturing. It is also a key factor affecting the transformer operating performance. The error of traditional method based on empirical formula estimate is large. In this paper, the dry-type power transformer core temperature field distribution of 1000 kVA rated capacity has been systematically studied using the sequential coupling method of ANSYS software based on finite element theory. The electromagnetic field distribution of the transformer has been extracted first, and then the analysis result of electromagnetic field can be as the load of the heat generation rate to obtain the core temperature field distribution. This method can be applied to the transformer design process in order to reduce the cost of the transformers design. Also, it can be used to the run equipment electromagnetic field and thermal field distribution analysis in order to improve the operational reliability of the transformer.