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  • 1
    Electronic Resource
    Electronic Resource
    Collective effects of interface roughness and alloy disorder in InxGa1−xN/GaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1724-1726 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The collective effects of alloy disorder and interface roughness on optical properties of InxGa1−xN/GaN multiple quantum wells (MQWs) have been studied. The results are compared with those of GaN/AlGaN MQWs and InGaN epilayers. InxGa1−xN/GaN MQWs emit a broad and asymmetrical photoluminescence (PL) band, while GaN/AlGaN MQWs and InGaN epilayers emit narrower and Gaussian-shaped PL bands. Furthermore, the decay of excitons at low temperatures in InxGa1−xN/GaN MQWs follows a nonexponential function even at the lower-energy side of the PL spectral peak, while those in GaN/AlGaN MQWs and in InGaN epilayers follow a single exponential function. Both alloy disorder and interface roughness have to be included in order to interpret the PL emission spectrum and the decay dynamics in InxGa1−xN/GaN MQWs. Important parameters of the InxGa1−xN/GaN MQWs, σx, σL, and dτ/dL, denoting the alloy disorder, the interface roughness, and the rate of changing of the exciton decay lifetime with well width, respectively, have been deduced. The method developed here can be used to determine σx, σL, and dτ/dL in any MQW systems with wells being alloy materials. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122258
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of well thickness and Si doping on the optical properties of GaN/AlGaN multiple quantum wells (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1368-1370 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Effects of well thickness and Si doping on the optical properties of GaN/AlGaN (MQWs) have been investigated by picosecond time-resolved photoluminescence (PL) measurements. Our results have yielded that (i) the optical transitions in nominally undoped MQWs with narrow well thicknesses (Lw〈40 Å) were blue shifted with respect to the GaN epilayer due to quantum confinement, however, no such blue shift was evident for the MQWs with well thicknesses larger than 40 Å, (ii) the band-to-impurity transitions were the dominant emission lines in nominally undoped MQWs of large well thicknesses (Lw〉40 Å) at low temperatures, and (iii) Si doping improved significantly the crystalline quality of MQWs of large well thicknesses (Lw〉40 Å). The implications of these results on the device applications based on III-nitride MQWs have been discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119896
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  • 3
    Electronic Resource
    Electronic Resource
    Optical properties of a high-quality insulating GaN epilayer (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3821-3823 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Picosecond time-resolved photoluminescence (PL) spectroscopy has been used to investigate the optical properties of an insulating GaN epilayer grown by metalorganic chemical vapor deposition on a sapphire substrate. Two emission lines at 3.503 and 3.512 eV in the continuous wave (cw) PL spectra observed at 10 K under a low excitation intensity (∼23 W/cm2) were identified as the band-to-band transitions involving the A and B valence bands, respectively. A third emission line at 3.491 eV was identified as a band-to-impurity transition involving a shallow donor. The PL decay behavior can be well understood with a model taking into account both the free carriers and impurities. The effective recombination lifetime of the band-to-band transition in GaN was found to be about 3.7 ns. Possible mechanisms for the band-to-band transition being dominant in this high quality insulating GaN epilayer have also been discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124191
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  • 4
    Electronic Resource
    Electronic Resource
    Plasma heating in highly excited GaN/AlGaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2476-2478 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved photoluminescence (PL) spectroscopy was used to investigate carrier distributions in a GaN/AlGaN multiple quantum well (MQW) sample under high excitation intensities necessary to achieve lasing threshold. Room temperature PL spectra showed optical transitions involving both confined and unconfined states in the quantum well structure. Analysis of the experimental results using a microscopic theory, indicates that at high excitation the carrier distributions are characterized by plasma temperatures which are significantly higher than the lattice temperature. The implications of our findings on GaN MQW laser design are also discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122487
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  • 5
    Electronic Resource
    Electronic Resource
    Optical properties of GaN/AlGaN multiple quantum well microdisks (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2898-2900 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An array of microdisks with a diameter of about 9 μm and spacing of 50 μm has been fabricated by dry etching from a 50 Å/50 Å GaN/AlxGa1-xN (x∼0.07) multiple quantum well (MQW) structure grown by reactive molecular beam epitaxy. Optical properties of these microdisks have been studied by picosecond time-resolved photoluminescence (PL) spectroscopy. Photoluminescence emission spectra and decay dynamics were measured at various temperatures and pump intensities. With respect to the original MQWs, we observe strong enhancement of the transition intensity and lifetime for both the intrinsic and barrier transitions. The intrinsic transition is excitonic at low temperatures and exhibits an approximate tenfold increase in both lifetime and PL intensity upon formation of the microdisks. This implies a significant enhancement of quantum efficiency in microdisks and a bright future for III-nitride microcavity lasers. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120209
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  • 6
    Electronic Resource
    Electronic Resource
    Optical modes within III-nitride multiple quantum well microdisk cavities (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1530-1532 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical resonance modes have been observed in optically pumped microdisk cavities fabricated from 50 Å/50 Å GaN/AlxGa1−xN(x∼0.07) and 45 Å/45 Å InxGa1−xN/GaN(x∼0.15) multiple quantum well structures. Microdisks, approximately 9 μm in diameter and regularly spaced every 50 μm, were formed by an ion beam etch process. Individual disks were pumped at 300 and 10 K with 290 nm laser pulses focused to a spot size much smaller than the disk diameter. Optical modes corresponding to (i) the radial mode type with a spacing of 49–51 meV (both TE and TM) and (ii) the Whispering Gallery mode with a spacing of 15–16 meV were observed in the GaN microdisk cavities. The spacings of these modes are consistent with those expected for modes within a resonant cavity of cylindrical symmetry, refractive index, and dimensions of the microdisks under investigation. The GaN-based microdisk cavity is compared with its GaAs counterpart and implications regarding future GaN-based microdisk lasers are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120573
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  • 7
    Electronic Resource
    Electronic Resource
    Optical resonance modes in InGaN/GaN multiple-quantum-well microring cavities (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2563-2565 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microrings of varying sizes have been fabricated from InxGa1−xN/GaN (x∼0.15) multiple quantum wells (MQWs). Photolithography and dry etching techniques including both ion-beam and inductively coupled plasma etching were employed to pattern the III–nitride MQW microrings. Individual microrings were optically pumped and optical resonance modes were observed. The observed mode spacings were consistent with those expected for whispering-gallery (WG) modes within a resonant cavity of cylindrical symmetry, refractive index, and dimensions of the rings under investigation. The results obtained from the microring cavities were compared with those of the III–nitride MQW microdisk cavities. Our results have indicated that resonance modes corresponding to the radial and the WG modes are simultaneously present in microdisk cavities, but only WG modes are available from the microring cavities. Implications of our results on future GaN-based microcavity light emitters have been discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125078
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  • 8
    Electronic Resource
    Electronic Resource
    Optimizing growth conditions for GaN/AlxGa1−xN multiple quantum well structures (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 864-866 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the optimal growth conditions for GaN/AlxGa1−xN multiple quantum well (MQW) structures by metal organic chemical vapor deposition. Optical properties of a set of GaN/AlxGa1−xN MQW samples grown under systematically varied growth conditions have been studied by employing picosecond time-resolved photoluminescence (PL) spectroscopy. The PL emission efficiency, the linewidth of the PL emission spectra, the ratio of the barrier emission intensity to the well emission intensity, and the temperature dependence of the PL decay lifetime of these GaN/AlxGa1−xN MQW structures have been measured and compared with each other carefully. Based on our studies, we concluded that the optimal growth conditions for GaN/AlxGa1−xN MQW structures are GaN-like rather than AlxGa1−xN-like or other conditions. The GaN/AlxGa1−xN MQW structures grown under the GaN-like growth conditions exhibited higher quantum efficiencies and narrower PL emission linewidths than those grown under other conditions. PL emission from barrier regions was not observed in the MQW structures grown under the GaN-like growth conditions, which is highly preferred for ultraviolet light emitter applications. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125610
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  • 9
    Electronic Resource
    Electronic Resource
    Well-width dependence of the quantum efficiencies of GaN/AlxGa1−xN multiple quantum wells (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3040-3042 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of GaN/AlxGa1−xN(x(approximate)0.2) multiple quantum wells (MQWs) with well widths, Lw, varying from 6 to 48 Å has been grown by metalorganic chemical vapor deposition under the optimal GaN-like growth conditions. Picosecond time-resolved photoluminescence spectroscopy has been employed to probe the well-width dependence of the quantum efficiencies (QE) of these MQWs. Our results have shown that these GaN/AlGaN MQW structures exhibit negligibly small piezoelectric effects and hence enhanced QE. Furthermore, GaN/AlxGa1−xN MQWs with Lw between 12 and 42 Å were observed to provide the highest QE, which can be attributed to the reduced nonradiative recombination rate as well as the improved quantum-well quality. The decreased QE in GaN/AlxGa1−xN MQWs with Lw〈12 Å is due to the enhanced carrier leakage to the underlying GaN epilayers, while the decreased QE in MQWs with Lw〉42 Å is associated with an increased nonradiative recombination rate as Lw approaching the critical thickness of MQWs. The implications of our results on device applications are also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126572
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of alloy disorder on the transport properties of AlxGa1−xN epilayers probed by persistent photoconductivity (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1728-1730 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of alloy fluctuations on the transport properties of AlxGa1−xN alloys (x∼0.35) have been probed through the use of persistent photoconductivity (PPC). In the PPC state, the electron mobility, μe, as a function of electron concentration, n, in a single sample can be obtained under controlled light illumination conditions. It was found that μe is a constant when n is below a critical value nc and it then increases with n at n〉nc. This mobility behavior was attributed to the effects of alloy fluctuations in AlxGa1−xN alloys. As a result, the initial PPC buildup kinetics seen in AlxGa1−xN alloys was quite different from those in better understood semiconductor alloys, such as AlGaAs and ZnCdSe, and is a direct consequence of the observed unique dependence of μe on n. From these measurements, the total density of the tail states below the mobility edge in the conduction band was estimated to be 1.46×1017 cm−3 in a Al0.35Ga0.65N sample. The results were compared with those in II–VI semiconductor alloys and their implications on III-nitride device applications were discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126149
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