Strain-induced polarization in wurtzite III-nitride semipolar layers

Abstract

This paper presents growth orientation dependence of the piezoelectric polarization of InxGa1−xN and AlyGa1−yN layers lattice matched to GaN. This topic has become relevant with the advent of growing nitride based devices on semipolar planes [A. Chakraborty et al., Jpn. J. Appl. Phys., Part 2 44, L945 (2005)]. The calculations demonstrate that for strained InxGa1−xN and AlyGa1−yN layers lattice matched to GaN, the piezoelectric polarization becomes zero for nonpolar orientations and also at another point ≈45° tilted from the c plane. The zero crossover has only a very small dependence on the In or Al content of the ternary alloy layer. With the addition of spontaneous polarization, the angle at which the total polarization equals zero increases slightly for InxGa1−xN, but the exact value depends on the In content. For AlyGa1−yN mismatched layers the effect of spontaneous polarization becomes important by increasing the crossover point to ∼70° from c-axis oriented films. These calculations were performed using the most recent and convincing values for the piezoelectric and elasticity constants, and applying Vegard’s law to estimate the constants in the ternary InxGa1−xN and AlyGa1−yN layers.

Comparative study of polar and semipolar (112¯2) InGaN layers grown by metalorganic vapour phase epitaxy

“…1 The reduction of PEs increases overlap between electron and hole wave-functions resulting in an increase of radiative recombination probability, which may overcome the "green gap" problem as well as enhance the performance of LEDs based on semi-polar nitrides. 2,3 Efficient green and yellow semipolar ð11 22Þ InGaN single quantum-well LEDs grown on free-standing ð11 22Þ GaN substrates with threading dislocation densities below 10 7 cm À2 have been recently demonstrated.…”

Non‐polar group‐III nitride semiconductor surfaces

“…This spontaneous polarization and additional discontinuities of the piezoelectric polarization arising from strained interfaces in heterostructures lead to electric fields, separating the electrons and holes in the active region of a device, and thereby reducing the internal quantum efficiency [5]. In order to elucidate this inherent property of wurtzite semiconductor heterostructures, growth on semi-and non-polar surfaces attracted intensive attention.…”

Exciton localization in semipolar (112¯2) InGaN multiple quantum wells

“…The large r E value of the (11 22) samples studied here is believed to derive from the anisotropic growth on the (11 22) surface 26,27,29 and the onset of relaxation in (11 22) nitrides. 28,31 The strong ELOC in m-plane MQW 18 and the (11 22) MQW samples studied here can be another reason that should be taken into account with the reduced polarization fields 4,5 to explain why non-/semi-polar MQW structures have a much shorter radiative lifetime compared to polar MQW. 4,[12][13][14]20 To investigate the Stokes-shift of the samples, PL spectra together with PLE absorption edge were measured at 10 K using the Xe-lamp excitation source (P ex $ 10 -5 W/cm 2 ).…”

“…3 To overcome these problems, one of the promising solutions is to grow InGaN QW structures as an active region in LEDs along nonpolar and semipolar surface orientations due to a reduction in the polarization fields. 4,5 For example, a stable photoluminescence peak energy has been observed for nonpolar a-plane (11 20) 6 and m-plane (10 10) Al 0.2 Ga 0.8 N, 7 irrespective of excitation power density employed. Though much research on a-plane 8 and m-plane 9 green InGaN LEDs grown on bulk GaN substrates has been reported, the results have not yet met expectations.…”