Mechanism of thermal degradation in GaInN/GaN quantum wells

Abstract

In this contribution we focus on degradation processes of GaInN multiple quantum wells (MQWs) used in laser structures grown by metallorganic vapor pressure epitaxy (MOVPE). The influence of ramp‐up time as well as the maximum temperature during growth of the barrier on the quantum well (QW) is investigated. Comparison of X‐ray and photoluminescence (PL) measurements implies that a sufficient thickness of a cover layer grown at low temperature is required to prevent degradation of the QW. In a next step samples were grown using an optimal thermal budget during growth of the active region to investigate the influence of capping layers. To improve crystalline quality of these layers high temperatures are required. Our measurements show that these high temperatures lead to a decrease in average indium concentration of the QWs. This decrease is temperature as well as time dependent (∝ √t) and can only explained by diffusion processes. The activation energies are in the range 0.7‐0.9 eV (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Indium incorporation in GaInN/GaN quantum well structures on polar and nonpolar surfaces

“…Additional in-plane scans allow a direct measurement of the in-plane lattice constants and complete our strain state analysis. From all measured quantities and the growth times we are finally able to calculate the QW thickness and In concentrations in a self-consistent recursion method [9]. The layer thicknesses obtained by this evaluation method are in very good agreement with TEM measurements.…”

“…However, this www.pss-b.com effect can be mostly prevented if the QW is covered by a 2 nm thin GaN layer before the growth temperature is increased. Additional experiments with different thermal budgets in capping layers also show that both high temperatures and long times at elevated temperatures lead to a decrease of the indium content [9].…”

“…Ramping the growth temperature in the GaN barriers can suppress the formation of pits and significantly improve the structural quality. However, a proper temperature budget has to be chosen to prevent the QWs from degradation [9].The reciprocal space maps of the asymmetric reflections reveal that the structures are (nearly) fully strained. Actually, for the nonpolar samples two reciprocal space maps were measured due to the anisotropic strain situation in these structures.…”

Origin of the “green gap”: Increasing nonradiative recombination in indium‐rich GaInN/GaN quantum well structures

“…Both x In and t QW were determined by high resolution X-ray diffractometry (HRXRD) using the method described in [3]. In all samples, the last GaN barrier is the uppermost layer.…”

X‐ray composition analysis of nonpolar GaInN/GaN multiple quantum well structures

“…Since in the step model the smallest unit of length is given by the thickness of one atomic layer, having determined the period length it suffices to know the QW thickness only to the thickness of one monolayer, i.e., about 0.3 nm, to obtain a reasonable simulation. So we use the well thickness calculated from growth times [17] together with the period length as a first approximation, choose the number of planes in the QW and barrier which fit these values best and then adjust the simulation by varying the indium concentration. This procedure is justified by a TEM investigation on sample S1 (Fig.…”