Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Abstract

Extremely weak surface emission from (0001) c -plane AlGaN multiple quantum well structure in deep-ultraviolet spectral region Valence-band splitting and band-gap reduction in ordered GaInAs/InPThe valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k Á p theory yields a critical relative aluminum concentration x c ¼ ð0:0960:05Þ for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with C 9 symmetry of b C 9 ¼ 0:85eV, and propose a possible bowing for the crystal field energy of b cf ¼ À0:12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al x Ga 1Àx N=Al y Ga 1Ày N quantum well structures is discussed for different compositions. V C 2014 AIP Publishing LLC. [http://dx.

Band gap bowing and optical polarization switching in AlGaN alloys

“…Given the difficulties in experimentally determining the degree of optical polarization, as discussed in detail in Ref. (), plus the uncertainties in AlGaN material parameters, our value is close to the reported experimental data.…”

“…Experimentally, Neuschl et al. () found, based on polarization dependent photoluminescence spectroscopy, the optical polarization to switch in the range . Netzel et al.…”

“…Neuschl et al. () used k p theory to correct for the effect of strain originating from the underlying substrate. In doing so they find an adjusted range of .…”

Anisotropic optical properties of semipolar AlGaN layers grown on m-plane sapphire

“…Few studies hint towards a nonlinear trend of D cf between the values for GaN and AlN. 9,19,20 When introducing a bowing parameter b cf and fitting to our experimental data, we find b cf ¼ À0:015 eV which is in magnitude and sign in agreement with results in Refs. 9 and 20.…”

“…5, left hand side). 9,18 The valence band distances for strain-free material can be written as 17 Computed relative oscillator strengths f i (i ¼ x; y; z) of interband transitions from the three valence sub bands (C 7þ ; C 9 , and C 7À ) for all investigated samples. The predominantly observable transitions for the two polarization directions y (E ?…”