Chemical etching‐induced defects in n‐type ZnSe crystal grown by physical vapor transport

Abstract

We have found with deep level transient spectroscopy that chemical etching induced two isolated point defects, E1(0.26 -0.31) and E2(0.20), in the near-surface region of n-type ZnSe single crystals. The etching effect on the traps in Br-doped ZnSe bulk crystals was studied by using 5% Br-methanol solution, and then the E1 trap density increased with the chemical etching time, and reached to maximum value of 5.3 × 10 13 cm -3 . The E1 trap was obtained in the samples etched in some kinds of acid solutions, Br-methanol solution, HCl, and HBr, but did hardly in NaOH alkali etchant. These results suggest that the E1 trap is induced during the chemical etching and diffuse into the interior of the crystals. From above etching effects, we propose a tentative identification that E1 and E2 traps arise from two kinds of hydrogen related defects. IntroductionThe applications of the wide band gap semiconductor ZnSe include the blue/green laser devices, and so far some ZnSe-based heterostructure devices have been demonstrated [1,2]. Consequently, both the heterovalency and the differences of the thermal expansion coefficients between the ZnSe epilayer and the GaAs substrates, however, make it difficult to reduce the defect density. While high quality homoepitaxial layers have been grown on ZnSe substrates by MBE [3], and the ZnSe-based LD and LED have been fabricated on the ZnSe substrates [4]. Therefore, the homoepitaxial growth is essential to realize high qualitative single crystal films suitable for the fabrication of opto-electronic devices. To prepare n-type and low-resistive ZnSe substrates, we grew Br-doped ZnSe single crystals by a physical vapor transport (PVT) method [5]. The crystals had a net donor concentration of 1.4 -4.1 × 10 17 cm -3 , and showed that the FWHM of XRD rocking curve ranged from 6.7 to 8.9 arcsec. The some electron traps were so far reported in bulk-ZnSe crystal [6][7][8]. The origin of the traps was assumed to be a complex of Se and/or Zn vacancy and residual impurities [7,8]. Moreover the traps with similar activation energy have repeatedly been observed in n-type ZnSe crystals grown by the different techniques [9][10][11]. Recently we have found two electron traps, E1(0.31) and E2(0.20), in Br-doped ZnSe by deep level transient spectroscopy (DLTS), then reported the E1 trap was localized near the sample surface [12]. More research on the role of the electron traps is needed to control the conductivity in bulkZnSe crystals, and make a contribution to the material designs. In this article, we investigated n-type PVT-ZnSe crystals using DLTS, and examined the etching effects of the traps.