Strain relaxation in graded InGaN/GaN epilayers grown on sapphire

Abstract

Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain that builds up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled, thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10-nm GaN layer grown at 750 °C and annealed at 1000 °C.

GaN/air gap based micro‐opto‐electro‐mechanical (MOEM) Fabry‐Pérot filters

“…The relaxation occurs more quickly in epilayers grown by MOCVD than by MBE, more gradual relaxation is expected above 20 nm and this would lead to less deformation of the GaN membrane; this is to be confirmed experimentally in the future with our in-house MOCVD [17]. Deformation of consequent GaN membranes was 25 % less than that of the 1 st GaN membrane based on the layer by layer analysis [18]. The differences of deformation between adjacent membranes are in the range of 2 to 15 nm.…”

Study of carrier dynamics and radiative efficiency in InGaN/GaN LEDs with Monte Carlo method

“…For the higher In composition, the lattice mismatch is larger and it is harder to get a good crystal film even if the substrate is dislocation free. Therefore, it has been suggested that one use a thick InGaN buffer layer [21] to reduce the lattice mismatch in the system. This could be a possible solution to enhance the device performance.…”

Dual wavelength InGaN/GaN multi-quantum well LEDs grown by metalorganic vapor phase epitaxy

“…One of the most important light-emitting active layers, InGaN/GaN single or multiple quantum wells, draw special attention because of its unique material characteristics and device performance. Despite the large density of defects, primarily threading dislocation that exist in the InGaN/GaN multiple quantum well (MQW) region, the radiative recombination efficiency is surprisingly high and LEDs can achieve an external efficiency as high as 20% [3][4][5][6][7][8].…”