DSC Studies of P-Doped A-Si:H
- PDF / 295,340 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 97 Downloads / 189 Views
DSC STUDIES OF
SHINJI MATSUO,
HIROYUKI NASU,
A-Si:H
P-DOPED
CHIKASHI AKAMATSU,
TAKESHI IMURA AND YUKIO
OSAKA Department of Electrical Engineering, Faculty of Engineering, Hiroshima University, Saijo, Higashi-Hiroshima, 724
Japan
ABSTRACT Differential scanning calorimetry (DSC) studies of P-doped hydrogenated amorphous silicon (a-Si:H) show characteristic behaviors of glass transition phenomena. The glass transition temperature (Tg) detected by DSC for each sample well agrees with the equilibration temperature (TE) determined by the temperature dependence of dc conductivity.
Regarding
the influence of hydrogen content, Tg decreases and heat energy absorbed in this reaction increases, as hydrogen content increases. The interpretation for these phenomena is successfully attempted by the simulation based on the excess heat capacity model caused by the equilibrium process of defects.
INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) is generally distinguished from melt-quenched glass semiconductors such as amorphous selenium (a-Se) and amorphous arsenic trisulfide (a-As 2 S3 ) on account of the absence of glass transition phenomena. However, the following relaxation phenomena have been recently pointed out by
Street et al. [1] for P-doped a-Si:H. Those are summarized as (1)At elevated temperatures above equilibration temperature (TE), the structure of samples attains a metastable thermal equilibrium and (2) Below TE, the structure slowly relaxes with temperature-dependent time constant.
Thus,
the structure of the samples
rapidly cooled can be frozen-in according to them. In conventional glasses, glass transition must be associated with endothermic thermal reaction.
Therefore,
DSC (differential scanning
calorimetry) can be quite useful to investigate and to compare this relaxation phenomena with the transition of the conventional glasses. Compared to DTA (differential thermal analysis),
the quite higher
resolution of DSC seems to be appropriate to measure the relaxation. Mat. Res. Soc. Symp. Proc. Vol. 115. &188Materials Research Society
In
298
we have briefly reported our successful DSC our previous report [21, experiments of detecting endothermic peak due to the glass transition of Pdoped a-Si:H.
This paper reports the detailed analysis of DSC curves
obtained and the relationship to the electrical relaxation, and preparation conditions.
to the
Further, the theoretical interpretation for these
phenomena is carried out.
EXPERIMENTAL PROCEDURE The P-doped a-Si:H samples were prepared by the substrate impedance tuning technique using grounded mesh 13] with the following conditions: substrate temperature Ts=300 ' 440C, and gas molar ratio PH3 /SiH4 =1.6x1O-2. From characteristic X-ray measurements of the analytical electron microscopy, the content of P in films was 2-3 wt.%. The temperature dependence of dc conductivity for the samples was measured to obtain TE for the present samples from room temperature to 200 *C in vacuum. For DSC measurements, the samples deposited on aluminum foil wer
Data Loading...
