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

✍ Scribed by B. Chatterjee; S. A. Ringel; R. Hoffman Jr.

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 600 KB
• Volume: 4
• Category: Article
• ISSN: 1062-7995
• DOI: 10.1002/(sici)1099-159x(199603/04)4:2<91::aid-pip124>3.0.co;2-e

✦ Synopsis

Dislocations and related point defect complexes caused by lattice mismatch currently limit the performance of heteroepitaxial InP cells by introducing shunting paths across the active junction and by the formation of deep traps within the base region. We have previously demonstrated that plasma hydrogenation is an eHective and stable means to passivate the electrical activity of such defects within heteroepitaxial InP layers. In this work, we present our first results on the hydrogen passivation of actual heteroepitaxial n'p andp'n InP cell structures grown on GaAs substrates by metal organic chemical vapor deposition (MOCVD). We have found that a 2-h exposure to a 13.56-MHz hydrogen plasma at 275°C reduces the deep level concentration in the base regions of both n'p and p+n heteroepitaxial InP cell structures from as-grown values of 5-7 x 1014 down to 3-5 x I 0 l 2 em-'. All dopants were successfully reactivated by a 400"C, 5-min anneal with no detectable activation of deep levels. Current-voltage (I-V ) analysis indicated a subsequent -100-fold decrease in reverse leakage current at 1 V reverse bias, and an improved built-in voltage for the p+n structures. In addition to being passivated, dislocations are also shown to participate in secondary interactions during hydrogenation. We find that the presence of dislocations enhances hydrogen &flusion into the cell structure and lowers the apparent dissociation energy of Zn-H complexes fvom 1.19 e V for homoepitaxial Zndoped InP to 1.12 e V for heteroepitaxial Zn-doped InP. This is explained by additional hydrogen trapping at dislocations subsequent to the reactivation of Z n dopants after hydrogenation.