Stress and density of defects in Si‐doped GaN

Abstract

We report a study by photoluminescence (PL), Raman scattering, and highly resolved X‐ray diffraction (HRXRD) of a series of Si‐doped n‐type GaN layers grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire (0001) with the carrier concentration of 2.3 × 1017 – 9 × 1018 cm–3. We found that the band gap reduction deduced from the PL spectra analysis is due to both band gap narrowing (BGN) effect and change of the nature of stress in the GaN:Si layers. The HRXRD spectra show that at high Si‐doping levels (>1.6 × 1018 cm–3) the GaN films become under tensile stress. Progressive decreases of the E2 Raman mode frequency with Si concentration confirm this observation. The stress induced E2 mode frequency shift is estimated to 1.6 cm–1/GPa. Additionally, dislocation densities are determined by HRXRD by employing a model that uses the line width of X‐ray rocking curves. Atomic force microscopy (AFM) is also used to investigate the defect surface structures of GaN:Si layers which are dominated by pinned steps and surface depressions related to threading dislocations. We find that dislocation densities given by AFM measurements are in agreement with those obtained from rocking curve line widths. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mg and Si dopant incorporation and segregation in GaN

“…18 cm À3 [1,2] to tensile strain that increases with increasing Si dopant concentration. Also, an increasing density and variety of dislocations have been reported with increasing Si doping [1].…”

Photoreflectance investigation of band gap renormalization and the Burstein–Moss effect in Si doped GaN grown by MOVPE

“…Using the mentioned deformation potentials values, E s Δ and E gcor are calculated and the results are summarized in Table 1. The sign change in the energy correction E s s Δ reveals a transition of the residual stress state in Si-doped GaN films from compressive to tensile as observed in earlier studies [17,30]. …”

“…For GaN, only little attention was paid to the interplay between BM and BGR effects. Furthermore, most of theoretical analyses about the optical band gap shift in GaN, assume the electron effective mass as a constant, based on parabolic band approximation [4,6,7,17]. However, the conduction band shows a nonparabolic nature in heavily doped material and the electron effective mass increases with carrier concentration [5,[8][9][10][11]18].…”

High‐Resolution X‐Ray Diffraction of III–V Semiconductor Thin Films

“…One plausible explanation is that the relaxation increases with Siinduced defects formed during the cool-down process [17,18]. Thus, we can assume that the incorporation of silicon leads to increase of the dislocation density in the GaN epilayer.…”