Cluster size and composition variations in yellow and red light-emitting InGaN thin films upon thermal annealing

Abstract

We study thermal annealing effects on the size and composition variations of indium-aggregated clusters in two InGaN thin films with photoluminescence ͑PL͒ in the yellow and red ranges. The methods of investigation include optical measurement, nanoscale material analysis, and theoretical calculation. Such a study is important for determining the relation between the band gap and the average indium content of InGaN. In one of the samples, the major part of the PL spectrum is shifted from the yellow band into the blue range upon thermal annealing. In the other sample, after thermal annealing, a broad spectrum covering the whole visible range is observed. Cathodo-luminescence ͑CL͒ spectra show that the spectral changes occur essentially in the photons emitted from the shallow layers of the InGaN films. Photon emission spectra from the deeper layers are essentially unaffected by thermal annealing. The spectral changes upon thermal annealing are mainly attributed to the general trend of cluster size reduction. This interpretation is supported by the CL, x-ray diffraction, and high-resolution transmission electron microscopy results. To obtain a basic physics picture behind the spectral blue shift upon thermal annealing in the yellow emission sample, we theoretically study the quantum-confinement effects of InGaN clusters based on a quantum box model. The theoretical results can generally explain the large blue shift of PL spectral peak position.

Optical properties of InGaN/GaN multiple quantum wells with trimethylindium treatment during growth interruption

“…Near the PL spectral peak in the early stage, there exist delayed slow rises for a few hundred ps. Similar temporal behaviors, attributed to exciton transfer between localized states, were observed in the InGaN/GaN system in our previously study [18,19]. In addition, compared with the untreated sample, the decay profiles corresponding to the same emission wavelength decay are faster for the TMIn-treated sample.…”

“…For both samples, the temperaturedependent PL peak positions show an S-shaped behavior. The S-shaped behavior has been attributed to the carrier dynamics associated with carrier localization in potential minimums [18,19]. Furthermore, Fig.…”

Structural and optical properties of Al x Ga1 − x N/Al y Ga1 − y N multiple quantum wells for deep ultraviolet emission

“…Figure 4 shows the MQWs' emission at different acceleration voltages (from top to bottom, the acceleration voltages [20], using the Monte Carlo method to simulate the relationship between the maximum electron penetration depth and the electron acceleration voltage, the detection depth of 3 keV acceleration voltage is about 90 nm, and 15 keV for 1300 nm. In the case of 3 keV acceleration voltage, the main emission peak near 285 nm for Al x Ga 1 -x N/Al y Ga 1 -y N MQWs and a wide blue-green emission peak, which may be related with the deep energy level of the Al atom in the high Al content AlGaN material, are observed.…”

Depth dependence of optical property beyond the critical thickness of an InGaN film

“…8 shows the decreasing CL spectral peak energy with depth in the sample under study. Note that the penetration depths of electron beam with energies of 3, 5, 8, and 15 keV are about 88, 210, 450, and 1300 nm, respectively [8]. Therefore, in Fig.…”

“…To release strain energy, indium aggregation and phase separation can usually result in nano-scale indium-rich clusters and compositional fluctuations [4][5][6]. In particular, when a perturbation is introduced, such as thermal annealing, spinodal decomposition will enhance the clustering process [7,8]. Besides the local aggregation phenomenon, a more global behavior, called indium pulling [9][10][11], was also discovered.…”