Rapid thermal annealing effects on the optical properties in strained CdTe (100)/GaAs (100) heterostructures

Abstract

The growth of CdTe thin films has attracted much interest because of their potential applications in the areas of solar energy conversion, gamma-ray detection, and electro-optic modulation due to their low thermal noise and large absorption coefficient [1–5]. CdTe epitaxial layers have been extensively grown because CdTe thin films can be useful buffer layers for the growth of Hg1−x Cdx Te epilayers [6–9]. However, since the growth of high-quality CdTe/GaAs heterostructures has inherent problems due to the large lattice mismatch ( a/a = 14.6% at 25 ◦C), studies of the structural and optical properties of CdTe/GaAs heterostructures are very important for achieving high-quality optoelectronic devices that can operate in the blue-green region of the spectrum [10]. In addition, studies of the effects of thermal annealing on the optical properties play a very important role in enhancing device efficiency, and systematic studies concerning rapid thermal annealing effects on the optical properties of the CdTe/GaAs heterostructures are still necessary if highquality heterostructures are to be obtained after thermal annealing [11]. This letter reports the dependence of the optical properties on the annealing treatment for CdTe thin films grown on GaAs (100) substrates by using molecular beam epitaxy. Photoluminescence (PL) measurements were carried out to investigate the optical properties and to determine the activation energy of the confined electrons existing at the donor state in the as-grown CdTe/GaAs heterostructures. Elemental Cd and Te with purities of 99.9999% were used as the source materials and were precleaned by repeated sublimation. Cr-doped and semi-insulating (100) GaAs substrates were degreased in warm trichloroethylene (TCE), rinsed thoroughly in deionized water, etched in a HF solution, and rinsed in TCE again. As soon as the chemical cleaning process was finished, the GaAs substrates were mounted onto a molybdenum susceptor. Prior to CdTe thin-film growth, the GaAs substrates were thermally cleaned at 600 ◦C for 5 min in situ in the growth chamber at a pressure of 10−10 Torr. The depositions of the CdTe epilayers were done on GaAs substrates by using the MBE technique