Electrophotographic Properties of n + -a-Si:H/a-Si:H/a-SiC:H Heterostructures
- PDF / 370,589 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 58 Downloads / 157 Views
ELECTROPHOTOGRAPHIC PROPERTIES OF n+-a-Si:H/a-Si:H/a-SiC:H HETEROSTRUCTURES S.M. PAASCHE AND G.H. BAUER Institut f. Phys. Elektronik, University of Stuttgart, Pfaffenwaldring 47, D-7000 Stuttgart-80, Federal Republic of Germany ABSTRACT For negative chapging electrophotographic applications a three layer heterostructure (Al/n -a-Si:H/a-Si:H/a-SiC:H) has been investigated. To some extent a separation of the function of charge storage by a high band gap amorphous silicon carbon alloy and of that of photogeneration of carriers and of sufficient photosensitivity in an intrinsic amorphous silicon film has been achieved. Due to a low injection of electrons from the surface into the a-SiC:H and a small thermal generation rate of carriers within the aSi:H film, the dark decay of the negative surface potential is dominated by space charge limited currents of holes. Thus a considerable difference in surface potential for negative and positive charging occurs, which is related to the difference in electron and hole mobility in a-Si:H. Since there is no remarkable barrier at the heterointerface a-Si:H/a-SiC:H an excellent injection of photogenerated holes into the a-SiC:H can be provided. INTRODUCTION Growing attention has been paid to the application of a-Si:H for photoreceptors /1-5/ in the last few years. The use of a-Si:H for electrophotographic devices results in several advantages compared to conventional materials like amorphous selenium and it's compounds, like higher photosensitivity in the 700-800 nm range, strong mechanical surface hardness (1500-2000 Vicker strength /6/) and excellent thermal stability up to the deposition temperature (550 K). However, in application for dielectric relaxa1ion _1yers like a-Se based films, the dark conductivity of a-Si:H (10 -10 -Q cm- ) is too high to get acceptable decay times and sufficient surface potentials. Shimizu et al. /4/ suggested to decrease the dark conductivity by incorporation of a small amount of oxygen and by B compensation doping. Furthermore blocking layers have been required in order to avoid carrier injection at the surface and at the back contact /1,7/. Nakayama et al. /5/ introduced a single layer structure compensated by boron doping and added 1-10% oxygen to silane during deposition for bipolar charging (dielectric relaxation layer). A further concept bases upon the separation of the function of charge storage by a high band gap a-SiC:H alloy (E =2.3 eV) and of photogeneration of carriers in an intrinsic a-Si:H film. Ths structure exhibits a considerable difference in positive and negative charge retention and initial surface potential /8/. DEPOSITION OF FILMS The electrophotographic structures (Al/n+-a-Si:H (300 A)/a-Si:H (0.5-18 #jm)/a-SiC:H (3 pm)) have been prepared in a dc glow discharge system, which has been explained in detail previously /8/. The total gas flow amounted to 10 - 20 sccm; the growth rate of a-Si:H (5 s/s) and a-SiC:H (3 A/s) has been determined by optical transmission and by SEM measurements.
Mat. Res. Soc. Symp. Proc. Vol. 70. , 1986
Data Loading...
