Contactless electroreflectance, in the range of 20 K<T<300 K, of freestanding wurtzite GaN prepared by hydride-vapor-phase epitaxy

Abstract

We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-m-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter of A exciton deduced for the Ga (5ϫ10 5 dislocation cm Ϫ2) and N (1ϫ10 7 dislocation cm Ϫ2) faces are 3 and 7 meV, respectively, indicating a lower defect concentration on the former face. The parameters that describe the temperature dependence of the interband transition energies of the A, B, and C excitons as well as the broadening function of the A and B features are evaluated. The results from an analysis of the temperature dependence of the broadening function of excitons A and B indicate that GaN exhibits a very large exciton-phonon coupling.

Temperature-dependent study of the band-edge excitonic transitions of Cu2ZnSiS4 single crystals by polarization-dependent piezoreflectance

“…The obtained values of E i (0),˛i andˇi corresponding to the excitonic transitions for Cu 2 ZnSiS 4 are listed in Table 2. For comparison purposes the numbers from previous reports on freestanding wurtzite WZ-GaN [20], GaAs [21], ZB-ZnSe [22] and ZB-ZnS [23] are listed in Table 2.…”

“…The fitted values for E i (0), a Bi , and Bi are given in Table 2, and the corresponding values for freestanding WZ-GaN [20], GaAs [21], ZB-ZnSe [22] and ZB-ZnS [23] are also listed in Table 2 The fitted values of the broadening parameters of the E ex ⊥ and E ex || features for Cu 2 ZnSiS 4 with representative error bars are displayed in Fig. 6.…”

Properties and preparation of high quality, free-standing GaN substrates and study of spontaneous separation mechanism

“…It is well known that the heteroepitaxial growth of GaN layers on foreign substrates (Al 2 O 3 , SiC, or Si) leads to a residual compressive/tensile strain in epitaxial layers. This strain can be present even in FS-GaN layers grown by HVPE [13]. Therefore, measurement of the excitons energy can be used to evaluate the presence and type of the residual strain in the GaN layers.…”

Photoreflectance study of GaN grown on SiN treated sapphire substrate by MOVPE

“…In order to extract the energy and the broadening parameter of observed excitonic transitions, experimental data were least-square fitted to the first derivative Lorentzian line shape functional form [31][32][33][34] given by:…”