A NEW ANALYSIS OF CAPACITANCE MEASUREMENTS ON 0.83 eV ELECTRON TRAP LEVEL IN GaAs

Abstract

The 0.83 eV electron trap level in n-VPE grown GaAs crystal has been characterized using capacitance-voltage (C-V) and capacitance-time (C-t) measurements. A Schottky barrier diode was preferred to p+ -n junction diode due to ease in fabrication in the laboratory. A film of In was deposited over n+-GaAs substrate (back surface) by the vacuum evaporation to make ohmic contacts. The current-voltage (I-V) characteristics were found to be linear after alloying the contacts at 450°C for about 3 minutes in Nitrogen atmosphere. The rectifying contacts were then obtained by the vacuum deposition of Gold (Au) over GaAs epitaxial layer after covering the sample with a metal mask. C-V measurements were performed on the diodes and trap activation energy (EA), capture cross- section (on) and trap concentration (Nt) were determined 'to be 0.56 eV, 13 6.3x10 cm and 0.4x 1015 cm-3 respectively at the room temperature. Afterwards, capacitance-time measurements were performed on the diode sample which led to the -13 2 evaluation of EA=(0.835+0.005) eV, v- n=(3+1)x10 cm and Nt=(3.5±0.5)x1015 cm-3 by short and long transient methods. A difference of (0.275+0.005) eV was found in trap level location by C-V and C-t measurements. The reason behind this discrepency in electron trap level location is assumed to be due to the capture of electrons (iv) from I' band to trap level in C-V measurements while emission of electrons takes place to L band of conduction band in C-t measurements. As the L band lies 0.295 eV above f' band, hence discrepency of (0.275+0.005) eV is well understood. The origin of level is not understood. It has been shown that the new analysis of C-t measurements using short transients is sufficient to characterize a trap rather than recording the complete transients. This is expected to save a lot of time and cost in the experimental work