Unusual properties of the RY3 center in GaN

Abstract

The investigation and identification of point defects in GaN is crucial for improving the reliability of lightemitting and high-power electronic devices. The RY3 defect with a characteristic emission band at about 1.8 eV is often observed in photoluminescence (PL) spectra of n-type GaN grown by hydride vapor phase epitaxy, and it exhibits unusual properties. Its emission band consists of two components: a fast (10-ns lifetime) RL3 with a maximum at 1.8 eV and a slow (100-300 μs lifetime) YL3 with a maximum at 2.1 eV and zero-phonon line at 2.36 eV. In steady-state PL measurements, the YL3 component emerges with increasing temperature from 90 to 180 K, concurrently with a decrease in the RL3 intensity. The activation energy of both processes is about 0.06 eV. In time-resolved PL, the YL3 intensity abruptly rises when the RL3 intensity begins to saturate. These and other phenomena can be explained using a model of an acceptor with two excited states. A delocalized, effective-mass state at about 0.2 eV above the valence band captures photogenerated holes. These holes transition to the ground state, which produces the RL3 component with a lifetime of ∼10 ns. Alternatively, they may nonradiatively transition over a 0.06 eV-high barrier to a localized excited state with a level at 1.13 eV above the valence band. Recombination of free electrons or electrons at shallow donors with the holes at this localized excited state is responsible for the YL3 component. The relative intensities of the RL3 and YL3 components are dictated by the probabilities of holes at the shallow excited state to transition to the ground or to the localized excited states. Transition metals and complex defects are considered as the main candidates for the RY3 center.

Photoluminescence from defects in GaN

“…The RL3, YL3, and BL3 bands are three emission bands from a single defect (called the RY3 center) and observed in GaN grown by hydride vapor phase epitaxy (HVPE). 22 Two other PL bands in undoped GaN produced by HVPE are the RL1 and GL1 bands. GaN samples grown by molecular beam epitaxy (MBE) at relatively low temperatures are often contaminated by Ca and exhibit a strong GLCa band.…”

“…The Cp for the RY3 defect is exceptionally high because holes are captured by a shallow effective-mass state near the VBM. 22 Donors capture holes less efficiently because they are neutral. The data for the GL1, BL2, and BL3 bands look reasonable.…”

On the Origin of the Yellow Luminescence Band in GaN

“…We attribute the YL Be band to transitions from shallow donors or the conduction band to an acceptor level located at 0.3 eV above the VBM. [8] The distinguishing feature of the YL Be band is two-step quenching with increasing temperature. In n-type GaN samples, the first step is observed at T % 100 K, and the second quenching begins at T % 200 K. [8,113] In semi-insulating GaN:Be samples, the quenching occurs by an abrupt and tunable mechanism, and two steps are always observed.…”

Current Status of Carbon‐Related Defect Luminescence in GaN

“…[28] In the yellow spectral region YL3 with E max ¼ 2.10 eV and a ZPL at 2.36 eV is tentatively proposed to originate from a transition metal impurity found in n-type GaN grown by HVPE. [29,30] 2.1. Low C Concentration: Carbon on N Site -C N Carbon in GaN is expected to preferentially occupy the N lattice site due to similar atomic radii.…”