As one of the important physical parameters in semiconductors, carrier lifetime is measured herein via a protocol employing the microwave photoconductivity decay method.
Carrier lifetime is an important parameter for semiconductor wave analysis and materials. We need a common method for aberration of carrier lifetime. Here, we introduce microwave photoconductivity decay so called micro-PCD.
micro-PCD is commonly out of date micro-PCD is commonly out of date because it is long conduct and long disruptive method. Another advantage of this method is insensitiveness to Which follows aberration of materials of any structures. Demonstrating the procedure will be Takato Asada, a student from my laboratory.
To begin this procedure, prepare an n-type 4H silicon carbide epilayer. Using an ultrasonic washer, wash the sample with acetone for five minutes, follow by water for five minutes. Subsequently, use a nitrogen gun to remove moisture on the sample surface.
Next, prepare one molar of sulfuric acid, hydrogen chloride, sodium sulfate, sodium hydroxide, or one weight percent of hydrofluoric acid. Prepare an aqueous solution to be measured. Then pour the aqueous solution into a quartz cell.
Transfer the prepared sample into the cell, and immerse it into the aqueous solution. To prepare the measuring equipment, turn on the power supply of the 266 nanometers pulsed laser to excite the light source. Then set the laser mode on standby.
Connect the pulsed laser and an oscillator with a BNC cable. Turn on the oscillator and input a 100 hertz pulse wave to the pulsed laser. Subsequently, connect a photodiode to the oscilloscope with the BNC cable for triggering the acquisition.
Then turn on the photodiode. Next, put on the safety glasses. Irradiate the pulse laser and place the aperture of the microwave wave guide on the optical path of the laser light at the direction perpendicular to the light.
Install a half mirror on the optical path of the pulsed laser and reflect the pulse laser to the photodiode. Afterward, turn on the oscilloscope and set the trigger threshold on a voltage that is sufficient to detect signal from the photodiode. Then check the trigger frequency with an oscilloscope and tune it if necessary.
Subsequently, set the laser mode on standby. Connect a schottky barrier diode in a microwave wave guide for reflected microwave detection and a signal input channel of the oscilloscope with a BNC cable. Next apply a 9.5 volts operating voltage to a gun diode.
Place the quartz cell on the stand in front of the aperture as close as possible and fix with tape. To measure the carrier lifetime, turn on the laser light oscillation and eradiate the light to the sample. Place a half-wave plate, a polarizer, and a power meter on the optical path.
Eradiate the pulse laser to the power meter. Check the excitation intensity of the laser. Then adjust the half-wave angle for the control of the excitation intensity.
Afterwards, remove the power meter from the optical path. Adjust the time and voltage scales of the oscilloscope so that the peak signal is displayed on the oscilloscope. Subsequently, adjust the amplitude and phase of the microwave through an E-H tuner.
Check the oscilloscope and look for the E-H tuner where the peak signal is at maximum. Failed adjustment of the E-H tuner result in signal lost. This step should be perform most carefully.
Now, compromised overtunings yield tuner records and incorrect measurement. Tuning failure cannot be confirmed in the data processes. Adjust the time scale of the oscilloscope and sketch a decay curve in the measurement area on the oscilloscope.
Average the signal for an arbitrary number of times to improve the signal-to-noise ratio. Then save the measurement data as an electronic file to a memory drive. To process the data, import the signal data to a personal computer and plot the decay curves obtained from the experiment as a function of time.
Calculate the average value of background noise level, subtract it from the decay signal, and plot it as a function of time. Find the peak value of the decay signal and then divide the decay signal by the peak value. This plot shows micro-PCD decay curves of the n-type 4H silicon carbide in the air and in aqueous solutions.
An excitation light of 266 nanometers was irradiated to the silicon phase of the 4H silicon carbide in aqueous solutions. The time constant of the decay curves was longer with the sample immersed into the acidic aqueous solutions, implying that acidic solutions passivated surface states on the silicon phase and reduced surface recombination of the excess carriers. Please keep in mind These current properties are soundproof.
With a measurement of high conductivity soundproof, the signal strengths will be small. In such cases, bifurcation of signal will be regrade. High temperature measurement can be performed by blowing hotware while pressing the sample on hot plate.
Through the high temperature measurement, we speculate properties of different 15 carrier lifetime. This method has been in proprietary into conventional semiconductor industry. With this method, we can characterize 40 ohms same conductive materials and their surface properties complementary.
The pulsed rays is hazardous. Be sure to use safety glasses and do not wear watches to prevent light reflection.
