CuInSe₂ epitaxial layers with sphalerite structure

Abstract

Bulk CuInSe, at 1083 K has a reversible phase transition of first order from the ordered chalcopyrite to the disordered sphalerite structure ( MOLLER et al. 1985). In epitaxial layers deposited on (111)-oriented GaAs and Ge substrates by the flash evaporation technique (SCHUMANN et al. 1978a(SCHUMANN et al. , 1980a) the sphalerite phase was observed already a t lower substrate temperatures (Tab. 1). This sphalerite structure is stable a t room temperature in contrast t o the bulk material and can be detected by reflection high energy electron diffraction (RHEED) technique. On { 100)-and {llO}-oriented substrate no sphalerite structure was found (TEMPEL et al.). It should be noted that parts of the sphalerite phase in the CuInSe, epitaxial layers are not detectable by RHEED beside the chalcopyrite structure. Therefore, it is possible that the layers consist of the sphalerite phase partially even a t lower substrate temperatures as given in Table 1. SCHUMANN, KUHNThe reason for this phenomenon is unknown so far. l n this paper it is tried to give an interpretation for the occurrence of the sphalerite phase in epitaxial layers at relatively low growth temperatures.Combined thermogravimetric and mass spectroscopic investigations showed that CuInSe, evaporates in a two-stage process according t o 2 CuInSe, (s) + CuzSe (6) + In,Se (g) + Se, (g) (HONLE, KUHN). At lower temperatures (up t o about 1360K) the gaseous phase consists of In,Se arid Se,. Therefore, these both compounds should occur too a t the reevaporation from the growing layers. I n accordance with these considerations, at substrate temperatures Ts 2 770 K the epitaxial layers showed a Cu excess in comparison with the stoichiometric composition (HOBLER et el.; SOMMER et al.).

Epitaxial CuInSe2 thin films grown by molecular beam epitaxy and migration enhanced epitaxy

“…Reaching 22.6% efficiency [1], they are the most efficient polycrystalline thin-film solar cells available today [2]. The epitaxial growth of CISe on single crystal substrates, including GaAs [3][4][5], Si [6], Ge [5,7] GaP [8], GaN [9], and ZnSe [10] has been investigated by different groups. Also the improvement of the growth mode with different deposition techniques [11][12][13] has been investigated to grow epitaxial layers of CuInSe 2 , in which a lattice-matched substrate results in a reduction of structural defects and roughness in the CISe films.…”

“…In situ RHEED images of the GaAs (001) surface after oxide removal by depositing In at T s = 530 °C for (a) the[1][2][3][4][5][6][7][8][9][10] and (b) the [110] azimuths. RHEED images after the deposition of ~1.5 nm (18 deposition cycles of (Cu+In) and Se) by MEE at 530 ºC for (c) [1-10], (d) [110], and (e) [100] azimuths with respect to the GaAs substrate.…”