Investigation of CuGaSe2/CuInSe2 double heterojunction interfaces grown by molecular beam epitaxy.

Sathiabama Thiru,Toshiki Makimoto,Atsushi Tackeuchi,Yoshiji Horikoshi,Masaki Asakawa,Kazuki Honda,Atsushi Kawaharazuka

doi:10.1063/1.4908229

Abstract

In-situ reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy. The streaky RHEED pattern and persistent RHEED intensity oscillations caused by the alternate deposition of migration-enhanced epitaxy sequence are observed and the growths of smooth surfaces are confirmed. RHEED observation results also confirmed constituent material interdiffusion at the heterointerface. Cross-sectional transmission electron microscopy showed a flat and abrupt heterointerface when the substrate temperature is as low as 400 °C. These have been confirmed even by X-ray diffraction and photoluminescence measurements.

Highlights

In-situ reflection high-energy electron diffraction (RHEED) observation and Xray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy
Chalcopyrite materials such as CuInSe2 (CIS), CuGaSe2 (CGS) and their mixed compounds CuIn1-xGaxSe2 (CIGS) have been of technological interest as thin film solar cell absorber layers.[1,2,3]. Their optical and electrical characteristics are quite unique and attractive. This material system could be applied to variety of semiconductor devices other than solar cells
Considering the large ∆EC in CGS/CIS quantum wells as shown in Fig. 1, electrons in the deep donors of barriers are expected to be activated into the conduction band of CIS, which would contribute to n-type conductivity

Summary

Introduction

In-situ reflection high-energy electron diffraction (RHEED) observation and Xray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy. There was a report about CGS growth using MBE method, the grown samples exhibited very low hole mobility.[11] In the MEE growth, Cu+In (Cu+Ga) deposition period, the RHEED specular beam intensity increased and reached its maximum at the end of the deposition period. During MEE growth, RHEED specular beam intensity showed oscillation with constant amplitude according to the deposition sequence.

Results

Conclusion