Optimization on Temperatures of Filament and Substrate for High-Quality Narrow Gap a-Si1-xGex:H Alloys Grown by Hot-Wire CVD

Conference · Thu May 01 00:00:00 EDT 2003

OSTI ID:15004245

Xu, Y; Nelson, B P; Williamson, D L; Gedvilas, L M; Reedy, R C; Iwaniczko, E

We improve narrow-bandgap (1.2< ETauc< 1.3 eV) amorphous silicon germanium (a-Si1-xGex:H) alloys grown by hot-wire chemical vapor deposition (HWCVD) by lowering both substrate and filament temperatures. We grew two series of films using a tungsten filament. First we systematically varied the filament temperature (Tf) from our standard temperature of 2150ýC down to 1750ýC, while fixing all other deposition parameters. Secondly we systematically varied the substrate temperature (Ts) from our previous optimized temperature of 350ýC down to 125ýC, while fixing all other deposition parameters including Tf= 1800ýC. Films with the best properties are grown with Tf< 1880ýC and Ts between 200ý-250ýC. Improvement of the material properties are characterized by improvements in the H-bonding, reduced microvoid density, and good photoresponse (for a given ETauc). There are about 15% more Ge-H bonds-passivating Ge-dangling bonds-relative to our previous work. The films are more compact due to microvoid reduction as measured by small-angle X-ray scattering (SAXS). We also fabricated solar cells with these optimized materials and obtained~3.58%-efficient devices without doing bandgap profiling yet. Due to the high optical absorption of these a-Si1-xGex:H (~1.25 eV bandgap) alloys, we need an i-layer that is only~1200ý thick to obtain a Jsc of~20 mAcm2. Additionally, we increased the GeH4 gas utilization relative to SiH4 from previous work, which was about 1:1 (GeH4 in gas to Ge in film). Under the current conditions, a 35% GeH4 gas fraction produces an a-Si1-xGex:H film with x= 0.7.

• Research Organization: National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC36-99-GO10337
• OSTI ID: 15004245
• Report Number(s): NREL/CP-520-33559; TRN: US201015%%431
• Resource Relation: Conference: Presented at the National Center for Photovoltaics and Solar Program Review Meeting, 24-26 March 2003, Denver, Colorado
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
ABSORPTION
ALLOYS
CHEMICAL VAPOR DEPOSITION
DEPOSITION
GERMANIUM
OPTIMIZATION
SCATTERING
SILICON
SOLAR CELLS
SUBSTRATES
TUNGSTEN
A-SIGE:H
HOT-WIRE CHEMICAL VAPOR DEPOSITION
SUBSTRATE TEMPERATURE
FILAMENT TEMPERATURE
H BONDING
MICROVOID DENSITY
PHOTORESPONSE
SMALL-ANGLE X-RAY SCATTERING
Solar Energy - Photovoltaics
Amorphous Silicon
Si Based Materials (not devices): Alloys (with Ge
C
etc.)
Devices: Other Solar Cells (SiGe
mc-Si)
Material Properties: Opto/Electronic
Material Properties: Point Defects
Material Properties: Structural
Vibrational
&amp; Elastic