Hydrogen passivation of n+p and p+n heteroepitaxial InP solar cell structures

Conference · Sun Oct 01 04:00:00 EDT 1995

OSTI ID:177658

Chatterjee, B; Ringel, S A; Hoffman, R Jr ^[1]

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1. Essential Research, Inc., Cleveland, OH (United States)

High-efficiency, heteroepitaxial (HE) InP solar cells, grown on GaAs, Si or Ge substrates, are desirable for their mechanically strong, light-weight and radiation-hard properties. However, dislocations, caused by lattice mismatch, currently limit the performance of the HE cells. This occurs through shunting paths across the active photovoltaic junction and by the formation of deep levels. In previous work the authors have demonstrated that plasma hydrogenation is an effective and stable means to passivate the electrical activity of dislocations in specially designed HE InP test structures. In this work, they present the first report of successful hydrogen passivation in actual InP cell structures grown on GaAs substrates by metalorganic chemical vapor deposition. The authors have found that a 2 hour exposure to a 13.56 MHz hydrogen plasma at 275 C reduces the deep level concentration in HE n+n InP cell structures from as-grown values of approximately 10(exp 15)/cm(exp {minus}3), down to 1-2 x 10(exp 13)/cm(exp {minus}3). The deep levels in the p-type base region of the cell structure match those of the earlier p-type test structures, which were attributed to dislocations or related point defect complexes. All dopants were successfully reactivated by a 400 C, 5 minute anneal with no detectable activation of deep levels. I-V analysis indicated a subsequent approximately 10 fold decrease in reverse leakage current at {minus}1 volt reverse bias, and no change in the forward biased series resistance of the cell structure which indicates complete reactivation of the n+ emitter. Furthermore, electrochemical C-V profiling indicates greatly enhanced passivation depth, and hence hydrogen diffusion, for heteroepitaxial structures when compared with identically processed homoepitaxial n+p InP structures. An analysis of hydrogen diffusion in dislocated InP will be discussed, along with comparisons of passivation effectiveness for n+p versus p+n heteroepitaxial cell types.

• Research Organization: National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
• OSTI ID: 177658
• Report Number(s): N--96-15042; NASA-CP--10180; NAS--1.55:10180; E--9943; NIPS--95-05337; CONF-9510288--
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
ATOMIC DISPLACEMENTS
CRYSTAL LATTICES
EPITAXY
HETEROJUNCTIONS
HYDROGENATION
INDIUM PHOSPHIDE SOLAR CELLS
P-N JUNCTIONS
PASSIVATION
RADIATION HARDENING