Thermal Stability of Crystallographic Planes of GaN Nanocolumns and Their Overgrowth by Metal Organic Vapor Phase Epitaxy

Abstract

Thermal annealing of top−down fabricated GaN nanocolumns (NCs) was investigated over a wide range of temperatures for ammonia-rich atmospheres of both nitrogen and hydrogen. It was found that in contrast to the annealing of planar GaN layers, where surface morphology change is governed purely by material decomposition, reshaping of GaN NCs is strongly affected by competition between different crystallographic facets, which in turn depends on ambient atmosphere and temperature. A qualitative mechanism explaining the observed behavior has been proposed. On the basis of the analysis of these annealing results, growth conditions suitable for either predominantly lateral expansion of the NCs turning their sidewalls into six well-defined vertical m-plane facets, or, vice versa, their infilling from the base regions between the NCs were determined. GaN NC arrays of increased filling factors as compared to the as top−down fabricated ones have been demonstrated using these optimized growth conditions.

Ultralow Dark-Current and Superhigh Detectivity Ultraviolet Photodetector Based on Freestanding GaN Nanobelt Array

“…Meanwhile, the light and the photogenerated carriers were efficiently confined to the NBs. The PD exhibits extremely high light on/off ratio >10 8 and linear dynamic range of 161 dB. This work provides a route for GaN NB array preparation, transfer, and application in high-performance UV PDs.…”

“…Ultraviolet (UV) photodetectors (PDs) can convert invisible UV radiation into electronic signal, thus having extensive applications such as secure communication, biomedical diagnosis, and personal health monitoring systems. − Coping with the hash and complex applied scenarios, stability and high performance are indispensable indexes for an ideal UV PD. , Gallium nitride (GaN) is one of the most ideal semiconductor materials for UV PD owing to its superior environmental stability, suitable bandgap, excellent optical absorption, etc. − Commercial heteroepitaxial GaN film is usually grown on silicon or sapphire substrates, with a buffer layer (BL) between them to relieve the lattice and thermal mismatch. − However, the development of GaN UV PD is severely hampered by the high-defect-density BL, which contains several leakage pathways and nonradiative recombination centers. Meanwhile, the rigid foreign substrates make it impossible to fabricate flexible devices. , …”

Etching of the SiGaxNy Passivation Layer for Full Emissive Lateral Facet Coverage in InGaN/GaN Core–Shell Nanowires by MOVPE

“…First, the addition of an UL results in the disappearance of the 450 nm emission. This could be explained by the fact that the growth rate of the a-planes responsible for the emission at this wavelength in the H 3 PO 4 SQW is faster than that of m-planes so that the a-planes disappear during the UL growth, 64 resulting in the 400 nm GaN m-plane emission being the only emission measured in the SQW + UL sample. A weak 450 nm shoulder can be noticed in the spectrum of the MQW sample and is visible in Figure 4c, which could be due to the emission from the first QW.…”

Reduction of threading dislocation density in top-down fabricated GaN nanocolumns via their lateral overgrowth by MOCVD

“…The final NC top height variation is not expected to substantially increase as the wet etch is highly anisotropic (NCs shrink laterally but no c-plane etch happens [34]) and the regrowth conditions (950°C, N 2 ambient, high V/III ratio) are chosen to minimize c-plane growth. Full details on the regrowth procedure will be published elsewhere [27]; however, the key feature is that the slow c-plane growth is determined by the fact that if no TMGa is supplied at the applied conditions, there is a strong decomposition of GaN from c-plane facets of GaN NCs [15]. Supplying of TMGa during the overgrowth step here simply slows down the decomposition, so that zero, or even a slightly negative, growth rate is expected for NC c-plane facets.…”

“…The arrays of GaN NCs were finally brought back to the reactor for annealing and regrowth at 950°C in nitrogen to form six vertical m-plane sidewall facets and laterally expand the NCs. The optimization strategy for the regrowth conditions and details of NC array regrowth process will be presented separately [27].…”