Time-resolved photoluminescence, positron annihilation, and Al0.23Ga0.77N/GaN heterostructure growth studies on low defect density polar and nonpolar freestanding GaN substrates grown by hydride vapor phase epitaxy

Abstract

Time-resolved photoluminescence (TRPL) and positron annihilation measurements, as well as Al0.23Ga0.77N/GaN heterostructure growth by metalorganic vapor phase epitaxy were carried out on very low defect density, polar c-plane and nonpolar m-plane freestanding GaN (FS-GaN) substrates grown by hydride vapor phase epitaxy. Room-temperature photoluminescence (PL) lifetime for the near-band-edge (NBE) excitonic emission of the FS-GaN substrates increases with increasing positron diffusion length (L+); i.e., decreasing gross concentration of charged and neutral point defects and complexes. The best undoped c-plane FS-GaN exhibits record-long L+ being 116 nm. The fast component of the PL lifetime for its NBE emission increases with temperature rise up to 100 K and levels off at approximately 1.1 ns. The result implies a saturation in thermal activation of nonradiative recombination centers. The surface and interface roughnesses for a Si-doped Al0.23Ga0.77N/GaN/Al0.18Ga0.82N/GaN heterostructure are improved by the use of FS-GaN substrates, in comparison with the structure fabricated on a standard GaN template. The emission signals related to the recombination of a two-dimensional electron gas and excited holes are recognized for an Al0.23Ga0.77N/GaN single heterostructure grown on the c-plane FS-GaN substrate.

Local lifetime and luminescence efficiency for the near-band-edge emission of freestanding GaN substrates determined using spatio-time-resolved cathodoluminescence

“…The best data for the macroarea PL measurement on similar HVPE FS-GaN (Ref. 19) and typical values observed for GaN templates are also plotted for reference. As shown, g eq int linearly increases with the increase in s 1 according to g eq int ¼ ð1 þ s R =s NR Þ À1 , where we assume that s R is an intrinsic value to a particular material 20 and that s CL is generally dominated by s NR at room temperature under the relation s À1…”

Stokes shift in semi-polar (112¯2) InGaN/GaN multiple quantum wells

“…13 The subsequent overgrowth process is carried out by MOCVD with a growth temperature, V/III ratio and pressure at 1120 C, 1600, and 75 Torr, respectively, followed by the growth of InGaN/GaN MQWs. Semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) InGaN/GaN MQWs with a wide spectral range have been grown, and their peak emission wavelengths span from 497 to 591 nm, covering the whole green and yellow spectral ranges. Detailed X-ray diffraction and transmission electron microscopy (TEM) measurements show the indium composition is from 27% to 47%, demonstrating a great enhancement in indium incorporation over either c-plane or non-polar orientation.…”

“…A single (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN layer with a thickness of 1.3 lm is grown on m-plane sapphire using our high temperature AlN buffer technique by MOCVD. 14 For the subsequent overgrowth, mask-patterned micro-rod arrays have been fabricated on the semi-polar GaN layer.…”

Temporally and spatially resolved photoluminescence investigation of (112¯2) semi-polar InGaN/GaN multiple quantum wells grown on nanorod templates

“…This has also been observed on InGaN/GaN MQWs grown on free-standing GaN substrates. [9][10][11][12][13] A standard two exponential component model is used to study excitonic dynamics, and thus TRPL traces [I(t)] can be described by [16][17][18] IðtÞ ¼ A 1 expðÀt=s 1 Þ þ A 2 expðÀt=s 2 Þ:…”