Correlation of structural and optical properties of AlGaN films grown on SiN-treated sapphire by MOVPE

Effects of the diameter of thermally generated nanopits on carrier dynamics in AlGaN/GaN heterostructures

“…3 as a function of the annealing temperature. The positive value of εxx indicates the tensile nature of the strain, in agreement with previous studies for AlGaN deposited on GaN/sapphire 4 , 7 . The tensil-strain value for the as-grown sample is about 5×10−4.…”

“…The positive value of ε xx indicates the tensile nature of the strain, in agreement with previous studies for AlGaN deposited on GaN/sapphire. 4,7 The tensil-strain value for the as-grown sample is about 5 × 10 −4 . After thermal treatment, the tensil-strain value first increases with increasing annealing temperature to reach a maximum of 2.6 × 10 −3 at 1100°C.…”

“…AlGaN ternary alloys have attracted increasing attention in the last decades due to their excellent physical properties, such as large and direct bandgap, high electron mobility, high thermal conductivity, high breakdown field, and great mechanical stability 1 – 5 In addition, when varying the Al content, the bandgap of AlGaN varies from 3.4 eV for GaN to 6.2 eV for AlN, covering a broad spectral range 5 – 8 This makes AlGaN and their based heterostructures very promising for the realization of a number of electronic and optoelectronic devices, such as high electron mobility transistors (HEMT), 9 – 11 metal–oxide semiconductor (MOS) HEMT, 12 MOS heterostructures field-effect transistor, 13 , 14 ultra-violate (UV) light-emitting diodes (LEDs), 15 – 18 and solar-blind UV photodetectors 19 …”

“…Yet, the performance of AlGaN-based devices has been limited by some challenging issues connected to the AlGaN layer quality, 4 , 8 , 22 e.g., the relatively low internal quantum efficiency, the poor p-type doping efficiency, and hardly achievable n- and p-type good ohmic contacts 8 , 23 . The primary factor responsible for the issues mentioned above is the presence of high dislocation and point-defect densities in the AlGaN epilayer due to heteroepitaxy on foreign substrates 4 , 15 . Isolated point defects and/or point defects coupled with dislocations create deep levels, act as scattering centers for light, and increase the nonradiative recombination rate 4 , 24 .…”

“…Hence, reducing point defects in AlGaN layers is the key to improving the performance of AlGaN-based devices. For this purpose, various strategies and growth techniques have been suggested, such as the epitaxial lateral overgrowth, 15 the SiN treatment of sapphire substrate, 25 the deposition of low-temperature GaN or AlN buffer layer, 26 and the insertion of high-temperature GaN template layer between the buffer layer and the AlGaN active layer 4 . Despite the noticeable improvement in the layer quality using the aforementioned methods, the density of point defects in AlGaN is still higher than the level aimed to reach the full potential of AlGaN-based applications and devices.…”