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

T

S

=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 τ

2

respectively.τ1=10ns and τ

2

=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.