Characterization of ordered structure for AlInP2 and GaInP2

• Main Authors: Wen-Chun Yeh, 葉文鈞
• Other Authors: Ying-Sheng Huang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/74741525848636086152

博士 === 國立臺灣科技大學 === 電子工程系 === 89 === We have characterized the AlInP2 and GaInP2 epilayers that exhibit different degree of ordering by using the polarization dependent piezoreflectance (PzR) measurements in the temperature range between 25 and 500 K. AlInP2 is an indirect wide band-gap semiconductor, while GaInP2 belongs to the direct one. Both AlInP2 and GaInP2 are lattice matched to GaAs. The samples studied were grown on Si-doped GaAs substrates by metalorganic chemical vapor deposition method. The effects of ordering on the direct band gap of AlInP2 and GaInP2 consist of two major features, namely, the reduction of band gap and the splitting of the fourfold degenerate valence-band maximum at the Γ point with a crystal-field energy. The ordering induced shift of the band gap and crystal-field splitting are quadratic functions of the long-range order parameter η. The polarized PzR measurements showed anisotropic character along the [110] and [ ] directions for the ordered samples. The PzR spectra were fitted using the first derivative of a Lorentzian line shape functional form. The direct band-to-band, valence-band splitting to band and spin-orbit splitting to band transition energies were accurately determined. The order-dependent direct-gap reduction and valence-band splitting in spontaneously ordered indirect-gap AlInP2 were determined by polarized PzR spectroscopy at room temperature. The experimentally deduced values of the ratio of band-gap reduction to crystal-field splitting for the perfectly ordered alloys, ζ = －ΔEg(1) / ΔCF(1) = 1.15. and the ratio of band-gap reduction to the ordering change of spin-orbit splitting between the perfectly ordered and random alloys, ξ = －ΔEg(1) / [ΔSO(1) －ΔSO(0)] = 8.24, are in good agreement with the recent theoretically calculated values of 1.13 and 13.5, respectively, by S. H. Wei and A. Zunger [S.-H Wei and A. Zunger, Phys. Rev. B 57, 8983 (1998)] but are much larger than those of the previous report by Schubert et al. [M. Schubert, B. Rheinländer, E. Franke, I. Pietzonka, J. Škriniarová, and V. Gottschalch, Phys. Rev. B 54, 17616 (1996)] using dark-field spectroscopy. We are confident that the more sensitive PzR technique offers more reliable results. And it is almost certain that dark-field spectroscopy measurements by Schubert et al. give an under estimate of ζ and ξ. The temperature dependent of the direct band-, crystal field splitting- and spin-orbit splitting- to conduction band transition energies which are denoted as Eg, Eg+ΔE12 and Eg+ΔE13 respective, at various temperatures were accurately determined for AlInP2 and GaInP2. The temperature dependence of these near direct band-edge critical points transition energies were analyzed by the Varshni expression and an expression containing the Boise-Einstein occupation factor for phonons. The parameters that describe the temperature variation of the transition energies were evaluated. The results showed a definite trend that these parameters increase with increasing ordering parameter η.