GD a-Si:H主光致发光带的时间分辨研究

本文研究了低温淀积(例如T:<150℃)的GD a-Si:H在77K的时间分辨光致发光谱和荧光衰退。光致发光谱显示非对称形,荧光衰退显示出最初的快衰退,较长时间后为慢衰退。在快衰退范围内可用两个时间常数逐点分析时间分辨光谱,把主发光带分解为两个近似高斯形的发光带,对于Ts=127℃的薄膜,两发光带峰值位置在t=0时分别为1.73和1.58eV。快衰退两带的时间常数分别为10和23ns。文中还初步讨论了这两个发光带的起因。

A TIME-RESOLVED STUDY OF THE MAIN PHOTOLUMINESCENT BAND OF GD a-Si:H

Using Ar+ laser pumped dye laser with cavity dumper,the time-resolved photoluminescence(PL)spectra and the luminescence decay of GD a-Si:H at 77K have been studied.The time-resolved PL spectra of an a-Si:H film deposited on quartz substrate at TS=127℃ are shown in Fig.1.The shape of the main PL,hand is asymmetrical.In 6600-8900Åregion,the PL decay at different wavelength is shown in Fig.2 and Fig.3.Each PL decay consists of,approximately,a fast exponential decay(t<20ns)followed by slower decay for longer times.The slope of the PL decay curves increases smoothly with decreasing wavelength in 6600-8400Åregion,but does not change in 8400-8900Åregion.According to these results,we suggest that the main PL band of GD a-Si:H is composed of two superimposed PL bands.In the fast decay region,PL band 1(high energy band)and 2(low energy band)have decay time constant τ1 and τ2,respectively.τ1=10ns and τ2=23ns were obtained from the decy cuarves at the two edges of the spectrum assuming that the decay at the edge is mainly determined by only one band.At a given wavelength A and time t,the PL intensity can be expressed aswhere I1(λ,t)and I2(λ,t)are the shape functions of PL band 1 and band 2 Respectively.Since the rate of change of I1(λ,t)and I2(λ,t)with t is much slower in comparison with an exponential function,expression(1)can be approximated byUsing exppression(2),the time-resolved spectra have been analysed from point to point by means of computer and we obtain I1(λ,0)and I2(λ,0),which have approximately Gaussian shape with peaks at 1.73 and 1.58eV,respectively,as shown in Fig.4.The red shift of PL band in a-Si:H is discussed.The results we have obtained show that the red shift of two peaks with time is not large,but the shift of the maximum values of their envelope with time is larger because the decay is faster for band 1(high energy band)than that for band 2(low energy band).These two PL bands may be attributed to the existence of the inho-mogeneous phases(grain like zone and grain boundary like zone)and have been discussed.