Defect Kinetics and Saturation in Amorphous Silicon-Germanium Alloys

Abstract

A quantitative comparison of defect kinetics under high-intensity light-soaking was carried out on a-Si:H and a-SiGe:H. A simple technique that ensures identical experimental conditions (generation rates and generation profiles) in samples of different bandgaps is demonstrated. It is shown that the apparent dependence on bandgap of the susceptibility to light-induced degradation is mainly due to changes in intrinsic carrier concentrations without the need to adhere to any structural changes.

The effects of native and light induced defects on optoelectronic properties of hydrogenated amorphous silicon–germanium (a-SiGe:H) alloy thin films

“…An important difference between these two figures is that the slope of [ls soak / ls anneal ] -1 is approximately two times higher than that of [a (1.0 eV) soak /a (1.0 eV) anneal ], indicating that defects causing the degradation of gls-products and increase of sub-bandgap absorption coefficient, a (1.0 eV), are not the same type of defects. Insignificant degradation kinetics of high Ge concentration alloys were also reported in previous investigations [10,15,36]. These results indicate that degradation kinetics in a-Si:H and a-SiGe:H alloys with Ge concentration up to 28% are similar in nature as in agreement with previous reports.…”

“…Contrarily, the density of deep defects in the bandgap increases with increased Ge alloying which finally degrades the lifetime of photogenerated carriers [3][4][5]. Even though earlier studies reported negligible Staebler-Wronski effect (SWE) in a-SiGe:H mainly due to poor material quality available at those times [6,7], high quality alloy films prepared after improved deposition systems exhibited a substantial SWE under light soaking similar to that intrinsic to pure a-Si:H [8][9][10][11][12][13][14][15][16]. For this reason, investigations of the light induced defect creation as well as native defects in the alloy as a function of Ge content has become an important issue to be understood and resolved both scientifically and technologically.…”

“…For this reason, investigations of the light induced defect creation as well as native defects in the alloy as a function of Ge content has become an important issue to be understood and resolved both scientifically and technologically. As compared to the research undertaken during the last three decades on the SWE seen in pure a-Si:H [17], only a small number of studies have been reported for the native and light induced defects in a-SiGe:H alloys [8][9][10][11][12][13][14][15][16]. Fundamental investigations of these defects have been carried out using electron spin resonance (ESR) [4,5,10], steady-state photoconductivity (SSPC) [8,12,18], modulated photoconductivity (MPC) [19,20], drive level capacitance profiling (DLCP) [21], and sub-bandgap absorption methods [3,8,18,[21][22][23][24].…”

Properties of polymorphous silicon–germanium alloys deposited under high hydrogen dilution and at high pressure

“…This conclusion would not be changed even if LS was performed under identical generation rates, and it is in agreement with previous works reporting that the rate for light-induced defect creation decreases with the band-gap narrowing. 31 We find very low values of for the low Ge content samples (xр0.15), of the order of a few seconds only, which are lower than usually found in the literature. 31,32 We finally note that our LS duration of 10 5 s was not sufficient to reach the fully saturated light-degraded photocurrent value for high Ge content samples ͑xϭ0.32 and 0.35͒.…”

Investigation of light induced degradation in hydrogenated amorphous silicon‐germanium alloy thin films using temperature dependent photoconductivity

“…However, increasing the Ge content of the alloy creates higher density of deep defects in the bandgap, which finally degrades the lifetime of photo generated carriers [3][4][5][6]. First investigations on the light induced degradation reported negligible Staebler-Wronski effect (SWE) [7,8], however, high quality alloy films prepared after improved deposition systems exhibited a substantial SWE under light soaking [9][10][11][12][13]. For this reason, investigations of the light induced defect creation as well as native defects in the alloy as a function of Ge content has become an important issue to be understood both scientifically and technologically.…”