In this study, we attempt to identify the presence of surface defects (SDs) at an n-type GaN surface after high-temperature growth and gain insight into their intrinsic features. To this end, first, we carefully investigate n-type GaN samples with different surface etching depths. Low-temperature photoluminescence (PL) spectra reveal that SDs are most likely nitrogen vacancies (VN) and/or VN-related point defects intensively distributed within ∼100 nm from the n-type GaN surface after a high-temperature growth. We investigate the effect of SDs on the internal quantum efficiency (IQE) of green light-emitting diodes (LEDs) by preparing GaInN-based green LEDs employing a surface-etched n-type GaN, which exhibits a prominent enhancement of the PL efficiency with an increase in the etching depth. This effect is attributable to the reduced non-radiative recombination centers in multiple-quantum-well active regions because the SDs near the n-type GaN surface are removed by etching. We discuss strategies of in situ engineering on SDs to further improve the IQE in GaInN-based green LEDs on the basis of the results presented in this study.

We aimed to further improve performances of GaN-based vertical cavity surface emitting lasers (VCSELs) by applying a combination of conducting distributed Bragg reflectors (DBRs) and lateral optical confinement structures simultaneously, generally used in GaAs-based VCSELs. Si-doped conducting AlInN/GaN DBRs and buried SiO 2 apertures were adopted in the GaN-based VCSELs. By comparing the VCSELs and micro LEDs to those with undoped non-conducting DBRs, we found that lower device resistances and more uniform lateral current distributions were obtained with the conducting DBRs. At the same time, the maximum light output power of 2.6 mW was observed from the VCSEL with the conducting DBR while 4.4 mW was obtained from the VCSEL with undoped DBR. Inferior characteristics of a GaInN quantum well active region was found on the Si-doped conducting DBR.

We demonstrated GaN-based vertical-cavity surface emitting lasers (VCSELs) with 5–30 μm wide nano-height cylindrical waveguide formed by BCl3 etching. A 5 nm-depth etching with BCl3 showed the most efficient current blocking at the interface of the etched p++-GaN and an ITO electrode among the cases with BCl3, Ar, or O2, which could be due to not only etching damages but also diffused B atoms into the etched surface. While room-temperature continuous-wave operations of the VCSELs with the large apertures were demonstrated, maximum light output power values of the large aperture VCSELs seemed limited by nonuniform current injection and device thermal resistances.