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Title: Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy

Abstract

The optical properties of Al-rich AlGaN/AlN quantum wells are assessed by excitation-power-dependent time-integrated (TI) and time-resolved (TR) photoluminescence (PL) measurements. Two excitation sources, an optical parametric oscillator and the 4th harmonics of a Ti:sapphire laser, realize a wide range of excited carrier densities between 10{sup 12} and 10{sup 21 }cm{sup −3}. The emission mechanisms change from an exciton to an electron-hole plasma as the excitation power increases. Accordingly, the PL decay time is drastically reduced, and the integrated PL intensities increase in the following order: linearly, super-linearly, linearly again, and sub-linearly. The observed results are well accounted for by rate equations that consider the saturation effect of non-radiative recombination processes. Using both TIPL and TRPL measurements allows the density of non-radiative recombination centers, the internal quantum efficiency, and the radiative recombination coefficient to be reliably extracted.

Authors:
; ; ; ;  [1]
  1. Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510 (Japan)
Publication Date:
OSTI Identifier:
22413145
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 7; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; ALUMINIUM NITRIDES; CARRIER DENSITY; ELECTRONS; EMISSION SPECTROSCOPY; EXCITATION; EXCITONS; GALLIUM NITRIDES; HOLES; OPTICAL PROPERTIES; PARAMETRIC OSCILLATORS; PHOTOLUMINESCENCE; QUANTUM EFFICIENCY; QUANTUM WELLS; REACTION KINETICS; RECOMBINATION; SAPPHIRE; SOLID-STATE PLASMA; TIME RESOLUTION

Citation Formats

Iwata, Yoshiya, Banal, Ryan G., Ichikawa, Shuhei, Funato, Mitsuru, and Kawakami, Yoichi, E-mail: kawakami@kuee.kyoto-u.ac.jp. Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy. United States: N. p., 2015. Web. doi:10.1063/1.4908282.
Iwata, Yoshiya, Banal, Ryan G., Ichikawa, Shuhei, Funato, Mitsuru, & Kawakami, Yoichi, E-mail: kawakami@kuee.kyoto-u.ac.jp. Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy. United States. doi:10.1063/1.4908282.
Iwata, Yoshiya, Banal, Ryan G., Ichikawa, Shuhei, Funato, Mitsuru, and Kawakami, Yoichi, E-mail: kawakami@kuee.kyoto-u.ac.jp. Sat . "Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy". United States. doi:10.1063/1.4908282.
@article{osti_22413145,
title = {Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy},
author = {Iwata, Yoshiya and Banal, Ryan G. and Ichikawa, Shuhei and Funato, Mitsuru and Kawakami, Yoichi, E-mail: kawakami@kuee.kyoto-u.ac.jp},
abstractNote = {The optical properties of Al-rich AlGaN/AlN quantum wells are assessed by excitation-power-dependent time-integrated (TI) and time-resolved (TR) photoluminescence (PL) measurements. Two excitation sources, an optical parametric oscillator and the 4th harmonics of a Ti:sapphire laser, realize a wide range of excited carrier densities between 10{sup 12} and 10{sup 21 }cm{sup −3}. The emission mechanisms change from an exciton to an electron-hole plasma as the excitation power increases. Accordingly, the PL decay time is drastically reduced, and the integrated PL intensities increase in the following order: linearly, super-linearly, linearly again, and sub-linearly. The observed results are well accounted for by rate equations that consider the saturation effect of non-radiative recombination processes. Using both TIPL and TRPL measurements allows the density of non-radiative recombination centers, the internal quantum efficiency, and the radiative recombination coefficient to be reliably extracted.},
doi = {10.1063/1.4908282},
journal = {Journal of Applied Physics},
number = 7,
volume = 117,
place = {United States},
year = {Sat Feb 21 00:00:00 EST 2015},
month = {Sat Feb 21 00:00:00 EST 2015}
}
  • The optical gain characteristics of Al-rich AlGaN/AlN quantum wells (QWs) were assessed by the variable stripe length method at room temperature. An Al{sub 0.79}Ga{sub 0.21}N/AlN QW with a well width of 5 nm had a large optical gain of 140 cm{sup −1}. Increasing the excitation length induced a redshift due to the gain consumption and the consequent saturation of the amplified spontaneous emission. Moreover, a change in the dominant gain polarization with Al composition, which was attributed to switching of the valence band ordering of strained AlGaN/AlN QWs at Al compositions of ∼0.8, was experimentally demonstrated.
  • Inhomogeneity in Al-rich AlGaN/AlN quantum wells is directly observed using our custom-built confocal microscopy photoluminescence (μ-PL) apparatus with a reflective system. The μ-PL system can reach the AlN bandgap in the deep ultra-violet spectral range with a spatial resolution of 1.8 μm. In addition, cathodoluminescence (CL) measurements with a higher spatial resolution of about 100 nm are performed. A comparison of the μ-PL and CL measurements reveals that inhomogeneities, which have different spatial distributions of a few- and sub-micron scales that are superimposed, play key roles in determining the optical properties.
  • Screw dislocations in Al-rich AlGaN/AlN quantum wells cause growth spirals with an enhanced Ga incorporation, which create potential minima. Although screw dislocations and their surrounding potential minima suggest non-radiative recombination processes within growth spirals, in reality, screw dislocations are not major non-radiative sinks for carriers. Consequently, carriers localized within growth spirals recombine radiatively without being captured by non-radiative recombination centers, resulting in intense emissions from growth spirals.
  • The internal quantum efficiency (IQE) of Al{sub 0.55}Ga{sub 0.45}N/AlN and Al{sub 0.55}Ga{sub 0.45}N/Al{sub 0.85}Ga{sub 0.15}N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ∼80% at a carrier density of 10{sup 18 }cm{sup −3} was achieved at ∼258 nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, inmore » addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures.« less
  • We have performed a detailed study of the impact of basal plane stacking faults (BSFs) on the optical properties of both a-plane InGaN/GaN quantum wells (QWs) and GaN template samples grown on r-sapphire. In particular, we have used polarised photoluminescence excitation spectroscopy (P-PLE) to investigate the nature of the low temperature recombination as well as extracting information on the valence band (VB) polarisation anisotropy. Our low temperature P-PLE results revealed not only excitons associated with intersubband quantum well transitions and the GaN barrier material but also a transition associated with creation of excitons in BSFs. The strength of this BSFmore » transition varied with detection energy across the quantum well emission suggesting that there is a significant contribution to the emission line width from changes in the local electronic environment of the QWs due to interactions with BSFs. Furthermore, we observed a corresponding progressive increase in the VB splitting of the QWs as the detection energy was varied across the quantum well emission spectrum.« less