In-rich InGaN∕GaN quantum wells grown by metal-organic chemical vapor deposition

Abstract

Growth mechanism of In-rich InGaN∕GaN quantum wells (QWs) was investigated. First, we examined the initial stage of InN growth on GaN template considering strain-relieving mechanisms such as defect generation, islanding, and alloy formation at 730 °C. It was found that, instead of formation of InN layer, defective In-rich InGaN layer with thickness fluctuations was formed to relieve large lattice mismatch over 10% between InN and GaN. By introducing growth interruption (GI) before GaN capping at the same temperature, however, atomically flat InGaN∕GaN interfaces were observed, and the quality of In-rich InGaN layer was greatly improved. We found that decomposition and mass transport processes during GI in InGaN layer are responsible for this phenomenon. There exists severe decomposition in InGaN layer during GI, and a 1-nm-thick InGaN layer remained after GI due to stronger bond strength near the InGaN∕GaN interface. It was observed that the mass transport processes actively occurred during GI in InGaN layer above 730 °C so that defect annihilation in InGaN layer was greatly enhanced. Finally, based on these experimental results, we propose the growth mechanism of In-rich InGaN∕GaN QWs using GI.

Optical and microstructural studies of atomically flat ultrathin In-rich InGaN∕GaN multiple quantum wells

“…19,20 However, in our UTIR InGaN QWs, most of misfit strain in InN was relieved at the very early stage of InN deposition by threading dislocation formation and also by atomic interdiffusion along growth direction ͑c-axis͒. 3,5 We believe that the formation of quite large localized centers in UTIR InGaN QWs is rather related with monatomic thickness fluctuation in QWs, not with indium composition undulation because general group-III adatom diffusion length at 730°C would not be in that high range of micrometer. 21 In Fig.…”

“…2,3 However, introduction of growth interruption before GaN capping made the formation of defect-annihilated and atomically flat UTIR InGaN layer possible in QWs because of active decomposition and mass transport process in Inrich InGaN layer. 3 UTIR InGaN QWs seem to be significantly free of internal electric field because of ultrathin thickness and/or high residual carrier concentration in the In-rich InGaN well, leading to internal electric field effect-free optical property. Also, an efficient carrier trapping into UTIR InGaN QWs is expected because excitons in GaN can be effectively localized at the In-rich InGaN well due to the large band offsets between the well and the barrier and smaller electronegativity of In than Ga, resulting in much stronger oscillator strength of excitons, as in the case of InAs/ GaAs system.…”

“…1 Recently, we have overcome these obstacles and have succeeded in growing high quality and atomically flat ultrathin In-rich ͑UTIR͒ InGaN / GaN quantum wells ͑QWs͒ with In composition of 60%-70% under quite an elevated growth temperature ͑730°C͒ of InN. 2,3 During In-rich InGaN QW growth, only trimethylindium ͑TMIn͒ and ammonia ͑NH 3 ͒ were supplied as precursors; however, strain relaxation and solid-state intermixing occurred, and defective In-rich InGaN QW with thickness fluctuation was formed instead of InN QW. 2,3 However, introduction of growth interruption before GaN capping made the formation of defect-annihilated and atomically flat UTIR InGaN layer possible in QWs because of active decomposition and mass transport process in Inrich InGaN layer.…”

“…2,3 During In-rich InGaN QW growth, only trimethylindium ͑TMIn͒ and ammonia ͑NH 3 ͒ were supplied as precursors; however, strain relaxation and solid-state intermixing occurred, and defective In-rich InGaN QW with thickness fluctuation was formed instead of InN QW. 2,3 However, introduction of growth interruption before GaN capping made the formation of defect-annihilated and atomically flat UTIR InGaN layer possible in QWs because of active decomposition and mass transport process in Inrich InGaN layer. 3 UTIR InGaN QWs seem to be significantly free of internal electric field because of ultrathin thickness and/or high residual carrier concentration in the In-rich InGaN well, leading to internal electric field effect-free optical property.…”

Violet-light spontaneous and stimulated emission from ultrathin In-rich InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

“…In addition, since the InN bandgap was reported as low as ϳ0.63 eV, 4,5 InN-based III nitrides have recently attracted much attention for extended potential application in a wide range of optoelectronic devices. For the realization of these devices, many groups have studied on the high quality InN and In-rich InGaN nanostructures, including quantum wells 6 ͑QWs͒ and quantum dots 7 grown by metalorganic chemical vapor deposition ͑MOCVD͒ and molecular beam epitaxy. However, device-quality In-rich InGaN nanostructures have not been obtained yet due to high equilibrium vapor pressure of nitrogen, 8 low dissociation temperature of InN, and large lattice mismatch between GaN and InN ͑ϳ11%͒.…”