InP tunnel junction for InGaAs/InP tandem solar cells
- International Stellar Technology, Inc., Houston, TX (United States)
Chemical beam epitaxy (CBE) has been shown to allow the growth of high quality materials with reproducible complex compositional and doping profiles. The main advantage of CBE compared to metalorganic chemical vapor deposition (MOCVD), the most popular technique for InP-based photovoltaic device fabrication, is the ability to grow high purity epilayers at much lower temperatures (450-530 C). The authors have previously shown that CBE is perfectly suited toward the fabrication of complex photovoltaic devices such as InP/InGaAs monolithically integrated tandem solar cells, because its low process temperature preserves the electrical characteristics of the InGaAs tunnel junction commonly used as an ohmic interconnect. In this work using CBE for the fabrication of optically transparent (with respect to the bottom cell) InP tunnel diodes is demonstrated. Epitaxial growth were performed in a Riber CBE 32 system using PH3 and TMIn as III and V precursors. Solid Be (p-type) and Si (n-type) have been used as doping sources, allowing doping levels up to 2 x 10(exp {minus}19)/cu cm and 1 x 10(exp {minus}19)/cu cm for n and p type respectively. The InP tunnel junction characteristics and the influence of the growth`s conditions (temperature, growth rate) over its performance have been carefully investigated. InP p(++)/n(++) tunnel junction with peak current densities up to 1600 A/sq cm and maximum specific resistivities (V(sub p)/I(sub p) - peak voltage to peak current ratio) in the range of 10(exp {minus}4) Omega-sq cm were obtained. The obtained peak current densities exceed the highest results previously reported for their lattice matched counterparts, In(0.53)Ga(0.47)As, and should allow the realization of improved minimal absorption losses in the interconnect InP/InGaAs tandem devices for Space applications.
- Research Organization:
- National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
- OSTI ID:
- 177649
- Report Number(s):
- N--96-15042; NASA-CP--10180; NAS--1.55:10180; E--9943; NIPS--95-05337; CONF-9510288--; CNN: NASW-4093
- Country of Publication:
- United States
- Language:
- English
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