Henning Feick

Contributions from gallium vacancies and carbon-related defects to the yellow luminescence in GaN

Carbon-doped GaN layers grown by molecular-beam epitaxy are studied with photoluminescence and positron annihilation spectroscopy. Semi-insulating layers doped with >1018 cm−3 carbon show a strong luminescence band centered at ∼2.2 eV (yellow luminescence). The absolute intensity of the 2.2 eV band is compared with the gallium vacancy concentration determined by positron annihilation spectroscopy. The results indicate that a high concentration of gallium vacancies is not necessary for yellow luminescence and that there is in fact a causal relationship between carbon and the 2.2 eV band. Markedly different deep-level ionization energies are found for the high-temperature quenching of the 2.2 eV photoluminescence in carbon-doped and reference samples. We propose that while the model of Neugebauer and Van de Walle [Appl. Phys. Lett. 69, 503 (1996)] applies for GaN of low carbon concentration, a different yellow luminescence mechanism is involved when the interstitial carbon concentration is comparable to or ...

Lattice-matched HfN buffer layers for epitaxy of GaN on Si

Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

Observation of a hydrogenic donor in the luminescence of electron-irradiated GaN

Excitonic luminescence of GaN after irradiation with 0.42-MeV electrons has been investigated in detail. The low-energy irradiation generates damage exclusively in the N sublattice. Additional bound-exciton lines are found and are shown to arise from a hydrogenic donor with a binding energy of 25 meV. The donor binding energy, bound-exciton localization energy, and bound-exciton lifetime are discussed in comparison with the values observed for ON and SiGa in the same sample. Nitrogen vacancies VN forming a hydrogenic donor state are suggested to be the most likely origin of this luminescence emission. Finally, a metastable behavior related to the damage-induced defects is reported and discussed in conjunction with interstitial-nitrogen-related defects.

Compression of the dc drain current by electron trapping in AlGaN/GaN modulation doped field-effect transistors

The frequently observed dc drain current compression of AlGaN/GaN modulation doped field-effect transistors is associated with partial loss of the two-dimensional electron gas caused by electron trapping. The behavior of the temperature-dependent electron concentration and persistent photoconductivity at low temperature in the AlGaN/GaN modulation doped heterostructure are indicative of the presence of DX centers in the AlGaN layer. Deep-level transient spectroscopy of the drain current reveals carrier trapping with activation energy of 0.28 eV. However, this value appears to be too small to explain the compression of the dc drain current or to attribute these traps to DX centers in AlGaN.

Luminescence energy and carrier lifetime in InGaN/GaN quantum wells as a function of applied biaxial strain

Continuous-wave and time-resolved photoluminescence of InGaN quantum wells are measured as a function of applied biaxial strain, which provides a unique means of altering the built-in polarization field in these structures. The direction and magnitude of the shift of the luminescence-peak energy are quantitatively analyzed within an analytical carrier separation model. It is found that the presently used piezoelectric coefficients of InGaN are not entirely consistent with our experimental results. Instead, consistent interpretation of our data requires the e13 and e33 piezoelectric coefficients of InN to be ∼15% larger than the commonly accepted values. Our analysis allows the assignment of an effective carrier-separation parameter to each investigated quantum-well sample, which quantifies the shift of the luminescence peak energy with the change in the polarization field. The effective carrier separation is found to be zero for narrow quantum wells (<1.5 nm) and asymptotically approaches the full quantum...

Elastic strain relief in nitridated Ga metal buffer layers for epitaxial GaN growth

Gallium nitride epitaxial layers were grown on sapphire by molecular-beam epitaxy using nitridated gallium metal films as buffer layers. The mechanical properties of the buffer layers were investigated and correlated with their chemical composition as determined by synchrotron radiation photoelectron spectroscopy. Biaxial tension experiments were performed by bending the substrates in a pressure cell designed for simultaneous photoluminescence measurements. The shift of the excitonic luminescence peak was used to determine the stress induced in the main GaN epilayer. The fraction of stress transferred from substrate to main layer was as low as 27% for samples grown on nitridated metal buffer layers, compared to nearly 100% for samples on conventional low-temperature GaN buffer layers. The efficiency of stress relief increased in proportion to the fraction of metallic Ga in the nitridated metal buffer layers. These findings suggest GaN films containing residual metallic Ga may serve as compliant buffer lay...

Band Gap of Hexagonal InN and InGaN Alloys

We present results of photoluminescence studies of the band gap of non-intentionally doped single-crystalline hexagona InN layers and In-rich InxGa1-xN alloy layers (0.36 < x < 1). The band gap of InN is found to be close to 0.7 eV. This is much smaller than the values of 1.8 eV to 2.1 eV cited in the current literature. A bowing parameter of b ≈ 2.5 eV allows one to reconcile our and the literature data for the band gap values of InxGa1-xN alloys in the entire composition region.

Generation-recombination low-frequency noise signatures in GaAs metal–semiconductor field-effect transistors on laterally oxidized AlAs

Low-frequency noise characteristics of GaAs-on-insulator metal–semiconductor field-effect transistors, for which the insulating buffer layer was produced by lateral wet-oxidation of AlAs, are studied. Devices with different gate widths were fabricated resulting in different overoxidation times for the AlAs layer. Three characteristic generation-recombination noise signatures are observed depending on the measurement temperature and the gate bias. A generation-recombination noise signature with energy level at Ec−0.69 eV is found to increase with the amount of overoxidation time. This near midgap trap shows an increase in concentration towards the oxide interface, and it is tentatively assigned to an arsenic-antisite-related defect known from previous studies as EB4. A possible mechanism for the formation and the microscopic origin of this defect are discussed.

Electrical and optical properties of carbon-doped GaN grown by MBE on MOCVD GaN templates using a CCl4 dopant source

Carbon-doped GaN was grown by plasma-assisted molecular-beam epitaxy using carbon tetrachloride vapor as the dopant source. For moderate doping mainly acceptors were formed, yielding semi-insulating GaN. However at higher concentrations p-type conductivity was not observed, and heavily doped films (>5 x 10{sup 20} cm{sup -3}) were actually n-type rather than semi-insulating. Photoluminescence measurements showed two broad luminescence bands centered at 2.2 and 2.9 eV. The intensity of both bands increased with carbon content, but the 2.2 eV band dominated in n-type samples. Intense, narrow ({approx}6 meV) donor-bound exciton peaks were observed in the semi-insulating samples.

AFM study of lattice matched and strained InGaAsN layers on GaAs

We studied strained & lattice matched InGaAsN, InGaAs, and GaAsN layers, grown on GaAs substrate with gas source molecular beam epitaxy. Nitrogen concentration and lattice-matched condition have been established from Vegards law with X-ray diffraction. Atomic force microscope measurement, at 22-monolayer thickness, shows different growth mechanism for each composition. Especially, a mesh-like surface morphology of lattice matched InGaAsN has been revealed in this study.