Structural, Optical and Thermal Properties of Bulk Zn1?xBexTe Crystals

Abstract

Bulk Zn 1-x Be x Te crystals were grown in the range extending up to x ¼ 0.12. Their structural, optical and photothermal properties were characterised using X-ray diffraction, photoluminescence (PL) and photoacoustic (PA) methods. The lattice constants are found to follow a linear dependence on x. Energy gap and thermal diffusivity were determined from photoacoustic spectra. The energy-gap increasing trend with rising beryllium content is in agreement with that reported for thin (Zn,Be)Te layers on InP substrate.Introduction Early theoretical studies [1,2] have shown that beryllium could be an attractive cationic substitution for ZnTe. A partial substitution of a cation (such as Zn or Cd) by Be improves the II-VI-based device properties because of highly covalent bonding and high cohesive energy in beryllium chalcogenides [3][4][5]. Therefore, it allows for the extension of structural and band-gap engineering of II-VI semiconductors towards lower lattice parameters and higher energy gaps. Beryllium is now applied as a component of II-VI heterostructures for blue light-emitting diodes, lasers and photodetectors. There is a number of papers on the properties of bulk and layered (Zn,Be)Se solid solution but relatively little information on tellurium based II-VI compounds with partial cationic substitution by Be atoms is available. Recent results show that Zn 1--x Be x Te is a promising material for p-type cladding layer of ZnCdSe/MgZnCdSe lasers on InP substrate [6]. (Zn,Be)(Te,Se) has been successfully applied in design of quantum wells [7]. ZnBeTe ternary alloy has been applied as a p-contact layer in II-VI lasers [8] and as a component of LEDs using an InP substrate [9]. High hole concentration (4.8 Â 10 18 cm --3 ) has been achieved in Zn 0.6 Be 0.4 Te layer (on InP substrate) exhibiting 2.97 eV band-gap energy [6]. As for the design of heterostructures the knowledge of bulk crystal properties is of fundamental importance, bulk ZnBeTe crystals have been grown and their properties are under investigation. Preliminary studies of luminescence and photoacoustic spectra of bulk Zn 1--x Be x Te crystals have been performed in [10] and [11], respectively. In this work, basic crystallographic, optical and thermal properties of bulk Zn 1--x Be x Te crystals grown by high pressure Bridgman method are reported.

Optical characterization of bulk Zn1−xBexTe crystals

“…According to literature data [16][17][18][19][20], the possible donors are Al substituting for Zn (Al Zn ) or tellurium vacancies (V Te ), and the acceptors are V Zn or Ag Zn . The emission band in the energy range from 2.0 to 2.3 eV was observed for intentionally undoped ZnTe bulk crystals [12,21], as well as those doped with Al and Cl by thermal diffusion [17] and implanted with Al + , Zn + and Ar + [16,20]. The three main PL bands (2,371 eV, 2.325 eV and 2.2 eV in ZnTe) were observed for all Zn 1−x Be x Te crystals investigated.…”

“…The crystal bar obtained was cut into plates of about 1 mm thickness and mechanically polished. The structure and composition of the sample were determined by x-ray methods [12]. X-ray investigations showed that the compound crystallizes in the sphalerite structure type.…”

“…As for the design of optoelectronic devices based on heterostructures the knowledge of bulk crystal properties is of fundamental importance. Preliminary studies of photoluminescence (PL), basic crystallographic, thermal properties and photoacoustic (PA) spectra of bulk Zn 1−x Be x Te crystals have been reported [10][11][12].…”

Electronic properties and charge density of Be x Zn1 − x Te alloys

“…These are derived by fitting the bandgaps at a number of symmetry points in the binary compounds. The lattice constants were taken from the X-ray measurements (Paszkowicz et al 2002) and 350 plane waves were used for the calculations.…”

Application of the Inhomogeneous Sample Model in Piezoelectric Photothermal Spectroscopy of Zn1-x BexTe and Cd1-xMnxTe Mixed Crystals

“…Apart from the shift of the energy gap of the crystals from 2.28 eV for pure ZnTe crystals, to an average value of 2.35 eV for mixed crystals with a beryllium content x = 0.07, the spectra showed a considerable change of the shape with the frequency of modulation. This fact indicated the possibility of the existence of the complex crystal structure of the samples [16][17][18][19]. These experimental PPT spectra were then the focus of modeling with the inhomogeneous sample model.…”