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24 Aug 1998

Volume 73, Issue 8, pp. 1017-1159

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Back-illuminated GaN/AlGaN heterojunction photodiodes with high quantum efficiency and low noise

Wei Yang, Thomas Nohova, Subash Krishnankutty, Robert Torreano, Scott McPherson, and Holly Marsh

Appl. Phys. Lett. 73, 1086 (1998); http://dx.doi.org/10.1063/1.122092 (3 pages) | Cited 38 times

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Back-illuminated GaN/AlGaN ultraviolet (UV) heterojunction photodiodes with high quantum efficiencies are demonstrated. Photovoltaic (zero bias) responsivity of 0.2 A/W at 355 nm was achieved. The improved efficiencies primarily arise from the use of AlGaN/GaN heterojunction in which photons are absorbed within the p-n junction thus eliminates carrier losses due to surface recombination and diffusion processes in previously reported homojunction devices. Very high dark impedance and large visible rejection ratio were obtained. These results indicate high quality GaN/AlGaN interface and efficient photocarrier collection in the photodiode. © 1998 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors

AlGaN/GaN high electron mobility field effect transistors with low 1/f noise

M. E. Levinshtein, S. L. Rumyantsev, R. Gaska, J. W. Yang, and M. S. Shur

Appl. Phys. Lett. 73, 1089 (1998); http://dx.doi.org/10.1063/1.122093 (3 pages) | Cited 35 times

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Low-frequency noise in the frequency region of 20 Hz to 20 kHz is investigated in AlGaN/GaN high electron mobility transistors (HEMTs) grown on SiC substrates. The noise spectra have the form of the 1/f (flicker) noise. The measured Hooge parameter is as low as 0.0001. This value is comparable with Hooge parameter values for commercial GaAs field effect transistors and approximately two orders of magnitude smaller than Hooge parameter value measured for AlGaN/GaN heterostructures grown on sapphire. The level of noise depends on the gate leakage current; the noise is much higher in devices with a high gate leakage current. The small measured values of the Hooge parameter are related to a smaller leakage current and to a better material quality of the devices on SiC substrates and to a high electron sheet density. The low levels of the 1/f noise in the AlGaN/GaN HEMTs on SiC substrates make them suitable for applications in communication systems. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena

Electronic structure of self-assembled InAs quantum dots in GaAs matrix

P. N. Brounkov, A. Polimeni, S. T. Stoddart, M. Henini, L. Eaves, P. C. Main, A. R. Kovsh, Yu. G. Musikhin, and S. G. Konnikov

Appl. Phys. Lett. 73, 1092 (1998); http://dx.doi.org/10.1063/1.122094 (3 pages) | Cited 55 times

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Capacitance–voltage characteristics have been measured at various frequencies and temperatures for structures containing a sheet of self-assembled InAs quantum dots in both n-GaAs and p-GaAs matrices. Analysis of the capacitance–voltage characteristics shows that the deposition of 1.7 ML of InAs forms quantum dots with electron levels 80 meV below the bottom of the GaAs conduction band and two heavy-hole levels at 100 and 170 meV above the top of the GaAs valence band. The carrier energy levels agree very well with the recombination energies obtained from photoluminescence spectra. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Dark current and infrared absorption of p-doped InGaAs/AlGaAs strained quantum wells

D. H. Zhang and W. Shi

Appl. Phys. Lett. 73, 1095 (1998); http://dx.doi.org/10.1063/1.122095 (3 pages) | Cited 15 times

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The dark current as a function of temperature and infrared absorption of the p-doped In0.15Ga0.85As/Al0.45Ga0.55As multiple quantum well structures grown by molecular beam epitaxy are investigated. The dark current Id of the structure is found to be basically symmetrical over a voltage range from −10 to +10 V. It is about 10−9 A at a bias of 1 V at 80 K, more than two orders of magnitude lower than that reported for p-doped GaAs/AlGaAs QW structures with the same size. It is also found that Id is proportional to T exp[−(EC–EF)/kT] at 70 K and above while at temperatures below 30 K it does not change significantly. The EC–EF decreases with the increase in bias in an exponential form, due likely to energy bandgap bending. A strong infrared absorption peaked at a wavelength of 10.7 μm is in excellent agreement with the estimated value of 10.4 μm. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Pz Photoconduction and photovoltaic effects

Band offsets at GaInP/AlGaInP(001) heterostructures lattice matched to GaAs

X. H. Zhang, S. J. Chua, and W. J. Fan

Appl. Phys. Lett. 73, 1098 (1998); http://dx.doi.org/10.1063/1.122096 (3 pages) | Cited 7 times

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In this work, the band offsets at the Ga0.5In0.5P/AlxGa0.5−xIn0.5P heterojunction lattice matched to (001) GaAs was calculated over the whole range of aluminum composition from x = 0.0 to 0.5 using the first-principles pseudopotential method with virtual crystal approximation. The valence band offset, VBO, varies with x as VBO = 0.433x eV, while the inferred conduction band offset CBO at Γ minimum (band-gap difference minus the valence band offset) varies in x as CBOΓ = 0.787x eV. Our results are in good agreement with the experimental data. © 1998 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Observation of excitonic transitions in InSb quantum wells

N. Dai, F. Brown, P. Barsic, G. A. Khodaparast, R. E. Doezema, M. B. Johnson, S. J. Chung, K. J. Goldammer, and M. B. Santos

Appl. Phys. Lett. 73, 1101 (1998); http://dx.doi.org/10.1063/1.122097 (3 pages) | Cited 12 times

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We report the observation of interband exciton transitions in InSb/AlxIn1−xSb multi-quantum-well samples. The exciton peaks are identified with the use of a simple quantum well model. The strain present in the InSb wells alters the spectrum significantly from that for unstrained III–V materials and makes it possible to use the exciton spectrum in determining the band offset. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Observation of confinement-dependent exciton binding energy of GaN quantum dots

Peter Ramvall, Satoru Tanaka, Shintaro Nomura, Philippe Riblet, and Yoshinobu Aoyagi

Appl. Phys. Lett. 73, 1104 (1998); http://dx.doi.org/10.1063/1.122098 (3 pages) | Cited 45 times

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The photoluminescence emission peak energy of GaN quantum dots was observed to shift to higher energy with decreasing quantum dot size. This effect was found to be a combination of a blueshift from the confinement-induced shift of the electronic levels and a redshift from the increased Coulomb energy induced by a compression of the exciton Bohr radius. From this observation, absolute values of the exciton binding energy as a function of quantum dot size are determined. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Luminescence of porous silicon in a weak confinement regime

G. Polisski, H. Heckler, D. Kovalev, M. Schwartzkopff, and F. Koch

Appl. Phys. Lett. 73, 1107 (1998); http://dx.doi.org/10.1063/1.122099 (3 pages) | Cited 25 times

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We report on luminescence properties of porous silicon emitting efficient light only a few tens of meV above the band gap of bulk Si. This emission band has a well-defined low-energy limit coincident with the position of the lowest possible luminescing exciton state of bulk silicon. The resonant photoluminescence spectrum exhibits all possible combinations of zero-phonon and momentum-conserving TA- and TO-phonon assisted absorption and exciton emission processes known for bulk silicon. We found that TO-phonon assisted processes give a major contribution to the light emission. We discuss the implications of these studies for the understanding of the origin of porous silicon photoluminescence. © 1998 American Institute of Physics.
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78.55.Mb Porous materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Highly anharmonic potential modulation in lateral superlattices fabricated using epitaxial InGaAs stressors

R. J. Luyken, A. Lorke, A. M. Song, M. Streibl, J. P. Kotthaus, C. Kadow, J. H. English, and A. C. Gossard

Appl. Phys. Lett. 73, 1110 (1998); http://dx.doi.org/10.1063/1.122100 (3 pages) | Cited 5 times

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A coherently strained stressor structure is used to create a one-dimensional periodic potential in the two-dimensional electron gas at a AlGaAs/GaAs heterointerface. We demonstrate that from magnetotransport the Fourier coefficients of the conduction band modulation can be determined. In contrast to conventional electrostatic patterning, “hard” potential modulation with dominant contributions of higher harmonics is achieved. In the regime of narrow stressor-stressor distance, the strain-induced potential modulation can be calculated analytically from elasticity theory. The calculated magnetoresistance which can be derived from the stressor-induced potential is in good agreement with the experimental data. © 1998 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Single-electron effects in heavily doped polycrystalline silicon nanowires

Andrew C. Irvine, Zahid A. K. Durrani, Haroon Ahmed, and Serge Biesemans

Appl. Phys. Lett. 73, 1113 (1998); http://dx.doi.org/10.1063/1.122101 (3 pages) | Cited 14 times

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We have observed single-electron charging effects in heavily doped polycrystalline silicon nanowires at 4.2 K. Wires of approximately 20 nm by 30 nm active cross section were defined by electron-beam lithography and thermal oxidation in standard polycrystalline silicon material. We have measured a Coulomb staircase and periodic current oscillations with gate bias, attributed to localized carrier confinement resulting from a statistical variation in the intergrain tunnel barriers. A sharp change in the current oscillation period is seen and we speculate that it is due to electrostatic screening of the gate bias by grain boundary defect states. © 1998 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.72.Mm Grain and twin boundaries
85.35.Ds Quantum interference devices
71.55.Cn Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.Fz Weak or Anderson localization
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Dynamics of phonon-assisted tunneling in a silicon degenerate pn junction

W. H. Richardson

Appl. Phys. Lett. 73, 1116 (1998); http://dx.doi.org/10.1063/1.122102 (3 pages) | Cited 1 time

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The charge distribution and junction voltage on an indirect-band-gap semiconductor tunnel junction (that is in parallel with a resistor and current source) were obtained by solution of the master equation. Expressions for the tunneling rate in a silicon degenerate pn junction are presented. Phonon-assisted tunneling permits relaxation of a requirement (that the external resistance be much larger than the resistance quantum) for the observation of single electron tunneling oscillations. Consequently, that process may enable observation of such oscillations in practical single junction circuits. © 1998 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
73.23.-b Electronic transport in mesoscopic systems
73.40.Gk Tunneling
85.35.Ds Quantum interference devices

Silicon di-interstitial in ion-implanted silicon

Young Hoon Lee

Appl. Phys. Lett. 73, 1119 (1998); http://dx.doi.org/10.1063/1.122116 (3 pages) | Cited 25 times

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A new Si di-interstitial model is derived from the Si-P6 electron paramagnetic resonance spectrum observed in neutron-, proton-, or ion-implanted silicon. Two Si interstitials lie in the {100} plane at a position considerably off from two tetrahedral interstitial sites nearby, sharing one Si lattice atom. The di-interstitial disappears at 170 °C annealing and can form the 〈110〉 interstitial chains which are considered to be a “building block” of the {311} extended defects frequently observed in ion-implanted Si.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
76.30.Lh Other ions and impurities
61.72.uf Ge and Si
61.80.Jh Ion radiation effects

First-principles exploration of possible trap terminators in SiO2

Ayumi Yokozawa and Yoshiyuki Miyamoto

Appl. Phys. Lett. 73, 1122 (1998); http://dx.doi.org/10.1063/1.122103 (3 pages) | Cited 16 times

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Oxygen vacancies (O vacancies) are considered to be charge trap centers in SiO2. This letter explores possible terminators of Si-dangling bonds associated with the O vacancies by performing first-principles total energy calculations. The present exploration is focused on the terminators which retain their chemical bonds after hole trapping. We have found that Cl atoms, NH and OH molecules firmly terminate the Si-dangling bond while H atoms are dissociated from a Si�H bond after hole trapping. The H dissociation is accompanied by the generation of gap states which can contribute to the leakage currents in the SiO2 films. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.55.-g Dielectric thin films
61.72.J- Point defects and defect clusters
71.55.Ht Other nonmetals
61.50.Lt Crystal binding; cohesive energy

Three-dimensional atom probe field-ion microscopy observation of Cu/Co multilayer film structures

D. J. Larson, A. K. Petford-Long, A. Cerezo, G. D. W. Smith, D. T. Foord, and T. C. Anthony

Appl. Phys. Lett. 73, 1125 (1998); http://dx.doi.org/10.1063/1.122104 (3 pages) | Cited 24 times

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Focused ion-beam milling has been used to fabricate field-ion specimens from a multilayer film structure containing 100 repetitions of a (Cu2 nm/Co2 nm) bilayer deposited directly onto a planar substrate. The as-deposited films showed a magnetoresistance ratio of ∼5% over a 250 Oe range at room temperature, and a coercivity of ∼60 Oe. The magnetic data suggest that the films are coupled ferromagnetically. Successful field-ion specimen preparation has allowed the observation of these layers by field-ion imaging and three-dimensional atom probe compositional analysis. Examination of the multilayer images reveals that, in some regions, the layers are nonparallel, but the interfaces are chemically quite sharp, with a diffuse interface region of ∼3 atomic layers. In addition, in some areas adjacent cobalt layers appear to be in contact. The fact that the layers are wavy suggests that the ferromagnetic coupling may be a result of Néel “orange peel” type magnetostatic coupling between adjacent cobalt layers. The relatively high coercivity may be a result of the poor layer planarity leading to a high number of domain wall pinning sites. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Influence of Si doping on characteristics of InGaN/GaN multiple quantum wells

Yong-Hoon Cho, J. J. Song, S. Keller, M. S. Minsky, E. Hu, U. K. Mishra, and S. P. DenBaars

Appl. Phys. Lett. 73, 1128 (1998); http://dx.doi.org/10.1063/1.122105 (3 pages) | Cited 52 times

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We have systematically studied the influence of Si doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy. The twelve- period MQWs were grown by metalorganic chemical vapor deposition. Si doping in the GaN barriers was varied from 1×1017 to 3×1019 cm−3. Information on the structural quality of the MQWs as a function of Si doping was extracted from the linewidth broadening of the higher-order superlattice satellite peaks measured in HRXRD. The HRXRD measurements indicate that increased Si doping results in better interface properties of the MQWs. PL and PLE measurements show a decrease in the Stokes shift with increasing Si doping concentration. The 10 K radiative recombination lifetime was observed to decrease from ∼30 ns (for n<1×1017 cm−3) to ∼4 ns (for n = 3×1019 cm−3) with increasing Si doping concentration. The reduced Stokes shift, the decrease in radiative recombination lifetime, and the increase in the interface quality indicate that Si doping results in a decrease in carrier localization at potential fluctuations in the InGaN active layers. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Linewidth of the infrared absorption spectra due to bound-to-continuum transition in GaAs/AlxGa1−xAs multiple quantum well structures

Yunpeng He, Q. S. Zhu, Z. T. Zhong, G. Z. Zhang, J. Xiao, Z. P. Cao, X. H. Sun, and H. Z. Yang

Appl. Phys. Lett. 73, 1131 (1998); http://dx.doi.org/10.1063/1.122106 (3 pages) | Cited 1 time

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We have observed an extremely narrow absorption spectrum due to bound-to-continuum transition in GaAs/AlxGa1−xAs multiple quantum wells (MQWs). Its linewidth is only about one tenth of the values reported previously. Our calculation indicates that the broadening of the excited state in the continuum has little contribution to the absorption linewidth. We have grown a sample whose MQW region contains two kinds of wells with a minor thickness inhomogeneity. Its resultant absorption linewidth is six times as large as that of homogeneous well sample, which is in good agreement with our theoretical analysis. Thus we can suggest that the wider absorption spectra reported by many authors may be due to the well width inhomogeneity. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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