Atomic-scale structure and electronic properties of GaN/GaAs superlattices

Goldman, R. S.; Feenstra, R. M.; Briner, B. G.; Osteen, Mark; Hauenstein, R. J.

doi:10.1063/1.117193

Cited by 54 publications

(24 citation statements)

References 14 publications

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“…lower, than others. We associate these darker unit cells with N atoms which are substitutional for As in the alloy layer; the N atom contrast is similar to that previously observed in delta-doped N layers in GaAs [9]. There appears to be two distinct gray levels for most of the N atoms in Fig.…”

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confidence: 60%

Arrangement of nitrogen atoms in GaAsN alloys determined by scanning tunneling microscopy

McKay

Feenstra

Schmidtling

et al. 2001

Applied Physics Letters

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The pair distribution function of nitrogen atoms in GaAs0.983N0.017 has been determined by scanning tunneling microscopy. Nitrogen atoms in the first and third planes relative to the cleaved (1 0) surface are imaged. A modest enhancement in the number of nearest-neighbor pairs particularly with [001] orientation is found, although at larger separations the distribution of N pair separations is found to be random.Considerable interest has developed in recent years concerning GaAsN and InGaAsN alloys with low N content, typically a few %. The large predicted band gap bowing in this system of highly mismatched anions leads to the possibility of considerable band gap reduction with modest N content [1,2]. Important applications include lasers with wavelength in the 1.3-1.55 µm range, as well as solar cells with band gap around 1.0 eV [3]. Generally speaking the GaAsN and InGaAsN alloys have displayed evidence of inhomogeneities, such as broad photoluminescence (PL) line widths, variable PL decay times, and short minority carrier diffusion lengths [4][5][6][7]. Such observations are often taken as an indicator of compositional fluctuations in the materials, although direct structural characterization of such fluctuations is lacking.In this work we use cross-sectional scanning tunneling microscopy (STM) to directly probe the arrangement of N atoms in GaAs 0.983 N 0.017 alloys. Nitrogen atoms of two distinct contrast levels are imaged, which we assign to occupation in the first and third surface planes relative to the (1 0) surface. From an accurate determination of the position of about 1000 N atoms in a continuous strip of alloy material, we compute the distribution function of pair separations. The arrangement of N atoms is found to be quite consistent with that expected from random occupation, with the exception that an enhanced occurrence of nearest-neighbor N pairs is found.The GaAsN alloys studied here were grown on GaAs(001) substrates by metal organic vapor phase epitaxy (MOVPE) at temperatures between 530 and 570 C using TMGa, TBAs or AsH3, and tertiarybutylhydrazine (TBHy) under hydrogen carrier gas. Additional details of the growth and characterization of the material can be found in Ref. [8]. The particular film studied here consists of a GaAs buffer layer followed by a GaAs 0.983 N 0.017 layer, a 52 nm thick GaAs spacer layer, a GaAs 0.972 N 0.028 layer, and a 370 nm thick GaAs cap layer. The thickness of the GaAsN layers was determined by high-resolution x-ray diffraction (HRXRD) to be about 18 nm; STM measurements of their thickness gave results of 14-19 nm depending on location in the wafer. The N contents quoted above were also determined by HRXRD; STM measurements for those quantities gave similar results. The GaAs substrate, buffer layer, and cap layer were doped with Si at a con-1 1°P ublished in Appl. Phys. Lett. 78, 82 (2001).

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supporting

confidence: 60%

Arrangement of nitrogen atoms in GaAsN alloys determined by scanning tunneling microscopy

McKay

Feenstra

Schmidtling

et al. 2001

Applied Physics Letters

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“…Some N related features are visible within about 0.5 eV of the conduction band edge. These have been observed previously by STS [18] and are due to a well known NAs acceptor level [19]. The appearance of these states was not uniform across the sample.…”

Section: Ingaasn Imaging and Spectroscopymentioning

confidence: 63%

Distribution of nitrogen atoms in dilute GaAsN and InGaAsN alloys studied by scanning tunneling microscopy

McKay¹,

Feenstra²,

Schmidtling³

et al. 2001

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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Nitrogen atoms in the cleaved (1 0) surfaces of dilute GaAsN and InGaAsN alloys have been studied using cross-sectional scanning tunneling microscopy. The distribution of nitrogen atoms in GaAs0.983N0.017 and In0.04Ga0.96As0.99N0.01 alloys is found to be in agreement with random statistics, with the exception of a small enhancement in the number of [001]-oriented nearest neighbor pairs. The effects of annealing on In0.04Ga0.96 As0.99N0.01 alloys has been studied by scanning tunneling spectroscopy. Spectra display a reduced band gap compared to GaAs but little difference is seen between as-grown versus annealed InGaAsN samples. In addition, voltage dependent imaging has been used to investigate second-plane nitrogen atoms.

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“…The large sizemismatches of the anions can result in a phase separation. Stable alloys are found to grow in only narrow composition ranges near the binary endpoints (miscibility gap) [1][2][3][4]. They exhibit anomalous composition dependent electronic properties, both in the As-rich limit and in the N-rich limit.…”

Section: Introductionmentioning

confidence: 98%

Stability and band gaps of As‐rich and N‐rich GaAsN alloys: Density‐functional supercell calculations

Jenichen

Engler

2004

Physica Status Solidi (b)

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Total energies and band gap energies of cubic cells with various arrangements of Ga 32 As 32Àn N n (n ¼ 0-8 and n ¼ 28-32 corresponding to 0.0-25.0% N and 12.5-0.0% As) are calculated using the density-functional supercell method. In the As-rich limit up to an exchange of 6.2% N isolated N atoms (maximum N distance) are the most stable arrangement and provide the typical reduction of the band gap energy from about 1.5 eV (GaAs) to about 1 eV caused by reduction of the N distance. For higher N content special N distributions are the most stable arrangements. GaN m clusters (m ¼ 2-4) and isolated N atoms are less stable. The band gap remains nearly constant at about 1 eV between 6.2 and 18.8% N. The good agreement between the experimental band gap energies and ones calculated for the most stable arrangements points out that the experimental distribution of the atoms is the thermodynamic equilibrium distribution. In the N-rich limit, linear As chains in [110] direction or fragments of them are the most stable arrangement. At 9.4% As the band gap disappears.

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Atomic-scale structure and electronic properties of GaN/GaAs superlattices

Cited by 54 publications

References 14 publications

Arrangement of nitrogen atoms in GaAsN alloys determined by scanning tunneling microscopy

Arrangement of nitrogen atoms in GaAsN alloys determined by scanning tunneling microscopy

Distribution of nitrogen atoms in dilute GaAsN and InGaAsN alloys studied by scanning tunneling microscopy

Stability and band gaps of As‐rich and N‐rich GaAsN alloys: Density‐functional supercell calculations

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