Photocurrent Sensitivities, Surface Color, and Auger Spectroscopy of Silicon Carbide (SiC) by Photoelectro-Chemical (PEC
- PDF / 371,631 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 115 Downloads / 184 Views
current through the wafer and solution. The positive terminal of the power supply is connected to SiC wafer by its ohmic contact (anode) in the Teflon electrochemical cell. The negative terminal of the power supply is connected to a platinum needle (cathode) immersed in the electrolyte. RESULTS The PEC process was used to etch n-type cubic and 6H SiC, p-type cubic and cubic pn junctions. Experiments have shown that the I/V characteristics of the SiC-electrolyte interface reveal a minimum etch voltage of 3 V and 4 V for n- and p-type 3C-SiC, respectively. Additionally, n-type 6H-SiC shows a minimum etch voltage of 3 V. For current-voltage measurements, dark and light currents were measured. The photocurrent equation is the current with UV light minus the current without UV light.. Auger spectroscopy determines the chemical composition of elements in sample and the resulting Si/C ratio chosen by measuring the appropriate peak to peak scaling values of Si and C respectively
with the ratio of 3 being a nominal value for SiC. From Auger spectroscopy, an oxide formation is present on n-type 3C-SiC where after etching a yellowish layer corresponds to a low silicon to carbon (Si/C) ratio with large photocurrents and a white layer corresponds to a high Si/C ratio with small photocurrents. Ptype 3C-SiC shows a grayish or silver layer with a low Si/C ratio and a green layer with a high Si/C ratio. Additionally, n-type 6H-SiC shows a brown or blue layer with a minimum etch voltage of 3 V. The blue layer suggests a low Si/C ratio where more Si removal means a carbon rich sample and the brown layer suggests a high Si/C ratio which means more C removal. The colors of the etched regions of SiC represent layers that have some degree of porousity formed by the electrochemical process. As a result, the photo-excitation allows control of the porousity and changes the electrical properties of SiC. The nature of these porous layers with its increased resisitivity can lead to the formation of devices. We have summarized the results in the following table: MATERIAL p-type 3C
AUGER RATIO Si/C 8/0.25, Hi---Pure Si
MINIMUM volts required 4
COMMENTS grey/green porous
___.____layers
n-type 3C
4/3
3
n-type 6H
6/2
3
3C pn
1/3---Lo, 9/3---Hi
3
white/yellow porous layers brown/blue porous layers white/yellow porous; stop etching
The PEC etching of p-type 3C-SiC was the simplest to do among the applications. The sample studied for p-type 3C is labeled as a15. P-type layers of 3 ýtm or greater were used. Some results in etching p-type 3C-SiC included a minimum etch voltage of 4 volts and etch rates as high as 0.67 tim/min. An important observation was that the light and dark currents were similar. This means that no Ultraviolet (UV) light is needed to etch p-type and the photocurrents were near zero. Dark methods of etching p-type would be appropriate because hole formation during the PEC process is generated easily in p-type material. Other interesting findings were the change in colors of the SiC in the etched regions. For instanc
Data Loading...
