Pulsed laser (266nm) photo-response data of HPSI Silicon-Carbide (4H-SiC) at millimeter wavelength

Published: 2 May 2023| Version 2 | DOI: 10.17632/pw9rkfj5fg.2
Biswadev Roy


We have used a contactless time-resolved millimeter wave conductivity (TR-mmWC) system (Roy et al., 2018) operable in the D-band to acquire the sample radiofrequency (RF) responses by registering the detected voltages due to photo-absorption while transmitting 120 GHz (2.498mm wavelength) 0.36 mW. This sample is a high purity semi-insulating (HPSI) 4H-SiC sample fabricated by Cree. Dutta et al. (2008), and Jones et al. (2011) have used this hexagonal 4H-SiC wafer to study its dielectric properties using an open resonator. They reported an index of refraction 3.099 at a resonance frequency 136.747 GHz, and a loss tangent 6.2 x 10-5. The resistivity of this sample is > 105 Ω-cm, and the disk surface is on the {0001} plane within < 0.5°. The 4H-SiC sample is a hexagonal polytype and is of commercial grade. The DC responses are collected only in transmission mode. The source for millimeter waves is a cavity stabilized IMPATT diode with beam diameter ~2.8mm. The excitation source (pump) is a 266nm pulsed laser beam obtained using 532nm wavelength ultrafast DPSS laser system (FWHM: 0.69ns). A non-linear optical beta-barium borate (BBO) crystal (> 3mm) BBO8080-SHG532(I)-AR (size 8x8x8.0mm, for Type I Second Harmonic Generation centered at 532nm). The BBO crystal generated 4HG of 1064nm. We used two metal reflectors (266nm) and then focused on to the sample with laser fluence (~10.4 µJ cm-2 with spot size of the order 89 mm2). This experiment was done to collect data on changes in RF voltages when photocarriers are created and subsequently decay when laser is turned off. In both RF and DC measurements, the probe beam frequency is kept fixed at 120 GHz and the detector fed signal is amplified 35.7 times before input to a Keysight DSO for averaging and storage. The DC through voltage is collected manually using a multimeter connected to the DC output of the bias-tee that is attached to the horn antenna fed Schottky ZBD detector. The DC response is collected only when the laser is turned off and the sample is in line with the probe beam with the probe beam hitting the sample surface normally. The RF output is also collected when the laser is turned off and this becomes the background signal due to extraneous noise sources present in the room. The background signal need to be subtracted from the photo response acquired when the laser is pulsed on to the sample with full intensity. These 2 files are ASCII-delimited comma separated variable (.csv) files. In both files, column 1 represents the delay (seconds) and column 2 is the RF voltage (Volts) after amplification. The data were collected on February 14, 2023 and the DC voltage in the free space probe line was recorded to be 355.1 mV. The DC voltage is 342.4 mV when the sample is inserted in line with the probe beam. During the photoconductivity data collection we pulsed the laser at a frequency of 9000 Hz.


Steps to reproduce

A 532nm DPSS pulsed laser beam (pulsed at 9 kHz) was passed through BBO crystal to obtain 4HG of 1064nm (266nm) pulsed laser beam and the beam was transported using metal reflectors and focused on to the sample. A probe beam using IMPATT diode source was collimated and focused onto the sample. The RF voltages are collected from a Schottky zero barrier diode detector and low-noise amplified 35.7 time before being averaged about 10,000 times which is stored as a .csv file. There are two files one as background collection (RF) when the sample is in line with the probe beam that is transmitted through the sample, but the laser is turned off and another time the RF transient due to laser excitation of the sample.


North Carolina Central University


Photovoltaics, Silicon Carbide