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Title: Structural and electronic studies of a-SiGe:H alloys

This report describes work to produce alloys of a-Si[sub 1-x]Ge[sub x]:H of improved photoelectronic quality by plasma-enhanced chemical vapor deposition (PECVD). The goal was to discover optimum preparation conditions for the end-component, a-Ge:H, to establish whether modification of the usual practice of starting from a-Si:H preparation conditions was advisable. Such modification, found to be necessary, gave films of a-Ge:H with efficiency-mobility-lifetime products ([eta][mu][tau]) 10[sup 2] to 10[sup 3] higher than were earlier available, in homogeneous environmentally stable material. Both a-Ge:H and a-Si[sub 1-x]Ge[sub x]:H of large x were studied in detail. Alloy material was shown to have [eta][mu][tau] 10[sup 2] larger than found earlier. However, just as the [eta][mu][tau] of a-Si:H decreases when Ge is added, so also the [eta][mu][tau] of these alloys with Si addition. By contrast, the ambipolar diffusion lengths, L[sub o] which are governed by the hole mobility, vary by only a factor of two over the whole alloy series. Using the experimental finding of a small valence band offset between a-Si:H and a-Ge:H compositional fluctuations on a 10-mm scale are suggested to explain the behavior of [eta][mu][tau] and L[sub o] The implications for eventual improvement of the alloys are profound, but require direct experimental tests ofmore » the postulated compositional fluctuations.« less
Authors:
 [1]
  1. (Harvard Univ., Cambridge, MA (United States))
Publication Date:
OSTI Identifier:
6633607
Report Number(s):
NREL/TP-411-5457
ON: DE93010021
DOE Contract Number:
AC02-83CH10093
Resource Type:
Technical Report
Research Org:
National Renewable Energy Lab., Golden, CO (United States); Harvard Univ., Cambridge, MA (United States)
Sponsoring Org:
DOE; USDOE, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; GERMANIUM ALLOYS; CHEMICAL VAPOR DEPOSITION; SILICON ALLOYS; SILICON SOLAR CELLS; FABRICATION; AMORPHOUS STATE; ELECTRICAL PROPERTIES; GLOW DISCHARGES; INTERMETALLIC COMPOUNDS; MICROSTRUCTURE; PROGRESS REPORT; SILICON; ALLOYS; CHEMICAL COATING; CRYSTAL STRUCTURE; DEPOSITION; DIRECT ENERGY CONVERTERS; DOCUMENT TYPES; ELECTRIC DISCHARGES; ELEMENTS; EQUIPMENT; PHOTOELECTRIC CELLS; PHOTOVOLTAIC CELLS; PHYSICAL PROPERTIES; SEMIMETALS; SOLAR CELLS; SOLAR EQUIPMENT; SURFACE COATING 140501* -- Solar Energy Conversion-- Photovoltaic Conversion; 360101 -- Metals & Alloys-- Preparation & Fabrication; 360104 -- Metals & Alloys-- Physical Properties