Electron mobility exceeding 104 cm2/V s in an AlGaN–GaN heterostructure grown on a sapphire substrate

Wang, T.; Ohno, Y.; Lachab, M.; Nakagawa, Daisuke; Shirahama, Tatsuo; Sakai, Shiro; Ohno, Hideo

doi:10.1063/1.124151

Cited by 68 publications

(35 citation statements)

References 8 publications

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“…[7][8][9]29,35,36 The increments in mobility due to photoexcitation at a fixed temperature can be attributed to the increased electron mean energy with an increasing carrier density in the 2DEG channel, which leads to an improved screening and thereby reduced scattering between the 2DEG electrons with the ionized donor impurities. 24,29 The 9 These results show that there are considerable compressive strains that exist in our GaN layers due to the mismatch between the epilayers.…”

Section: Resultsmentioning

confidence: 99%

“…5,6 High-quality AlGaN/GaN heterostructures have been shown to contain two-dimensional electron gas ͑2DEG͒, which has attracted special interest due to its potential applications in high mobility transistors operating at high power and high temperature levels. [7][8][9][10] The device structures are usually grown on highly lattice-mismatched substrates, such as sapphire, 11 SiC, 12 or Si. 13 It still remains difficult to obtain a high-quality GaN epilayer because of the large lattice mismatch ͑ϳ14% for sapphire and ϳ3.5% for SiC͒ as well as the difference in the thermal expansion coefficients ͑ϳ80% for sapphire and ϳ3.2% for SiC͒ between the GaN film and sapphire and SiC substrates.…”

Section: Introductionmentioning

confidence: 99%

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The persistent photoconductivity effect in AlGaN/GaN heterostructures grown on sapphire and SiC substrates

Arslan

Bütün

Li̇şesi̇vdi̇n

et al. 2008

Journal of Applied Physics

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In the present study, we reported the results of the investigation of electrical and optical measurements in Al x Ga 1−x N / GaN heterostructures ͑x = 0.20͒ that were grown by way of metal-organic chemical vapor deposition on sapphire and SiC substrates with the same buffer structures and similar conditions. We investigated the substrate material effects on the electrical and optical properties of Al 0.20 Ga 0.80 N / GaN heterostructures. The related electrical and optical properties of Al x Ga 1−x N / GaN heterostructures were investigated by variable-temperature Hall effect measurements, photoluminescence ͑PL͒, photocurrent, and persistent photoconductivity ͑PPC͒ that in turn illuminated the samples with a blue ͑ = 470 nm͒ light-emitting diode ͑LED͒ and thereby induced a persistent increase in the carrier density and two-dimensional electron gas ͑2DEG͒ electron mobility. In sample A ͑Al 0.20 Ga 0.80 N / GaN/ sapphire͒, the carrier density increased from 7.59ϫ 10 12 to 9.9ϫ 10 12 cm −2 via illumination at 30 K. On the other hand, in sample B ͑Al 0.20 Ga 0.80 N / GaN/ SiC͒, the increments in the carrier density were larger than those in sample A, in which it increased from 7.62ϫ 10 12 to 1.23ϫ 10 13 cm −2 at the same temperature. The 2DEG mobility increased from 1.22ϫ 10 4 to 1.37ϫ 10 4 cm −2 / V s for samples A and B, in which 2DEG mobility increments occurred from 3.83ϫ 10 3 to 5.47ϫ 10 3 cm −2 / V s at 30 K. The PL results show that the samples possessed a strong near-band-edge exciton luminescence line at around 3.44 and 3.43 eV for samples A and B, respectively. The samples showed a broad yellow band spreading from 1.80 to 2.60 eV with a peak maximum at 2.25 eV with a ratio of a near-band-edge excitation peak intensity up to a deep-level emission peak intensity ratio that were equal to 3 and 1.8 for samples A and B, respectively. Both of the samples that were illuminated with three different energy photon PPC decay behaviors can be well described by a stretched-exponential function and relaxation time constant as well as a decay exponent ␤ that changes with the substrate type. The energy barrier for the capture of electrons in the 2DEG channel via the deep-level impurities ͑DX-like centers͒ in AlGaN for the Al 0.20 Ga 0.80 N / GaN/sapphire and Al 0.20 Ga 0.80 N / GaN/ SiC heterojunction samples are 343 and 228 meV, respectively. The activation energy for the thermal capture of an electron by the defects ⌬E changed with the substrate materials. Our results show that the substrate material strongly affects the electrical and optical properties of Al 0.20 Ga 0.80 N/GaN heterostructures. These results can be explained with the differing degrees of the lattice mismatch between the grown layers and substrates.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The persistent photoconductivity effect in AlGaN/GaN heterostructures grown on sapphire and SiC substrates

Arslan

Bütün

Li̇şesi̇vdi̇n

et al. 2008

Journal of Applied Physics

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“…The undoped GaN/AlGaN heterostructure used in this work (J401) was grown by MOCVD on a sapphire substrate [5]. A 2 mm undoped GaN layer was grown on a 25 nm GaN buffer layer and capped with 120 nm Al x Ga 1Àx N (x ¼ 0:18).…”

Section: Methodsmentioning

confidence: 99%

Energy Relaxation by Warm Two-Dimensional Electrons in a GaN/AlGaN Heterostructure

Stanton

Kent

Cavill

et al. 2001

phys. stat. sol. (b)

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The rate of energy loss per electron, P e , by a two-dimensional electron gas in an GaN/AlGaN heterostructure has been measured as a function of electron temperature, T e , in the range 0.4-35 K. A combination of zero and high magnetic field electrical transport measurements were used to determine T e as a function of the power dissipated in the device. It was found that P e / T n e , with n % 5 at the lowest temperatures, T e ( 2 K, while for higher temperatures, T e > 10 K, n ! 1. The experimental results are compared with numerical calculations of the energy relaxation rate. In the range of temperatures studied, emission of piezoelectrically coupled acoustic phonons was found to be the dominant energy relaxation mechanism.Introduction The process of hot carrier energy relaxation is of fundamental importance to the performance of all semiconductor electronic and optoelectronic devices. Measurement of energy relaxation rates provides information about the electron-phonon interaction which is of use in modelling device behaviour. Energy relaxation by hot two-dimensional (2D) carriers has been extensively studied in GaAs heterojunctions and quantum wells and Si MOS devices [1]. However, to date, there has been much less work with the aim of examining this process in GaN and its alloys.Recently Lee et al. [2] have reported measurements of the energy relaxation by warm 2D electrons in a GaN/AlGaN heterojunction. The temperature dependence of the amplitude of Shubnikov-de Haas (SdH) magnetoresistance oscillations was used as a thermometer for the electron temperature, T e . However, these measurements were limited by the technique to the electron temperature range T e < 4 K. Stanton et al. [3] studied the energy relaxation rate in bulk (3D) GaN samples using zero-field transport measurements to determine T e . In the low mobility samples used, this technique was applicable to a wide range of electron temperature, 1.5 K < T e < 300 K. However, in higher mobility samples, where phonon scattering makes a significant contribution to the mobility in the temperature range of interest, the technique must be used with caution [4].The main aim of the work described in this paper was to use the zero-field transport techniques to extend the measurements of Lee et al. to higher electron tempera-

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“…According to the calculation of Leung et al [19] , when the dislocation density is in the range of N DIS = 10 8 -10 10 cm −2 , only 10%-50% of the energy states will be occupied (f DIS = 0.1-0.5), so f DIS = 0.3 is adopted in the calculation. In some undoped AlGaN/GaN structures with low Al content, it is observed that the low temperature 2DEG mobility increases with Al content [20] . The DIS scattering may be one of the principal factors underlying the phenomena.…”

Section: Resultsmentioning

confidence: 98%

The mobility of two-dimensional electron gas in AlGaN/GaN heterostructures with varied Al content

Zhang

Hao

Zhang

et al. 2008

Sci. China Ser. F-Inf. Sci.

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The mobility of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures changes significantly with Al content in the AlGaN barrier layer, while few mechanism analyses focus on it. Theoretical calculation and analysis of the 2DEG mobility in AlGaN/GaN heterostructures with varied Al content are carried out based on the recently reported experimental data. The 2DEG mobility is modeled analytically as the total effects of the scattering mechanisms including acoustic deformation-potential, piezoelectric, polar optic phonon, alloy disorder, interface roughness, dislocation and remote modulation doping scattering. We show that the increase of the 2DEG density, caused by the ascension of the Al content in the barrier layer, is a dominant factor that leads to the changes of the individual scattering processes. The change of the 2DEG mobility with Al content are mainly determined by the interface roughness scattering and the alloy disorder scattering at 77 K, and the polar optic phonon scattering and the interface roughness scattering at the room temperature. The calculated function of the interface roughness parameters on the Al content shows that the stress caused AlGaN/GaN interface degradation at higher Al content is an important factor in the limitation of the interface roughness scattering on the 2DEG mobility in AlGaN/GaN heterostructures with high Al content.

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Electron mobility exceeding 104 cm2/V s in an AlGaN–GaN heterostructure grown on a sapphire substrate

Cited by 68 publications

References 8 publications

The persistent photoconductivity effect in AlGaN/GaN heterostructures grown on sapphire and SiC substrates

The persistent photoconductivity effect in AlGaN/GaN heterostructures grown on sapphire and SiC substrates

Energy Relaxation by Warm Two-Dimensional Electrons in a GaN/AlGaN Heterostructure

The mobility of two-dimensional electron gas in AlGaN/GaN heterostructures with varied Al content

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