The Design Of High-frequency Photoconductivity Decay Minority Carrier Lifetime Tester

As the microelectronics industry development, the quality of the materials and devices have higher requirements, the measurement of minority carrier lifetime is treated more seriously. Minority carrier lifetime is an important parameter for semiconductor materials and devices, which have an impact to the forward voltage drop of semiconductor devices, switching speed and diodes'luminous efficiency. Therefore, it is of great significance for the semiconductor device manufacturing and other industries to measure the parameter accurately.There are many minority carrier lifetime test methods, including the DC photoconductivity decay, quasi-steady state photoconductivity decay, high-frequency photoconductivity decay and the microwave reflection photoconductive decay. The article have a comparative analysis to the several representative minority carrier lifetime method, and concluded that high-frequency photoconductivity decay most suitable for laboratory research. The advantage is less demonding of the geometry of the sample, do not have to make ohmic contact and also non-contact, non-destructive to measure the samples' minority carrier lifetime, less sample contamination.This paper focuses on high-frequency photoconductivity decay minority carrier lifetime test system. Test system consists of analog circuit and microcontroller parts. The analog circuits parts include 20MHz high-frequency source generating circuit, power amplifier circuit, and the detector circuit. MCU PIC16F877 microcontroller is the core selection, which is responsible for signal acquisition, data analysis and data output. SPI mode and I2C mode of the MSSP module, CCP module's input capture mode and PWM output mode have been used. The system software design use MPLAB IDE v8.10 and C programming language.The designed high-frequency source circuit can produce 20MHz sine wave, the peak after peak value can up to±5V through sine wave power amplifier, the microcontroller program debugging is correct, and finally making into the PCB. By testing and debugging, the circuit can generate 20MHz,±2.5V sine wave, it can get the basic design requirements. However, the waveform is not stability for the reason of high-frequency source. The improved method is to separate high-frequency source into a single PCB with a metal seal.