The bulk and 2-dimensional (2D) electrical transport properties of heavily Mg-doped p-type GaN films grown on AlN buffer layers by Metal Modulated Epitaxy are explored. Distinctions are made between three primary p-type conduction mechanisms: traditional valence band conduction, impurity band conduction, and 2D conduction within a 2D hole gas at a hetero-interface. The bulk and 2D contributions to the overall carrier transport are identified and the relative contributions are found to vary strongly with growth conditions. Films grown with III/V ratio less than 1.5 exhibit high hole concentrations exceeding 2 × 1019 cm−3 with effective acceptor activation energies of 51 meV. Films with III/V ratios greater than 1.5 exhibit lower overall hole concentrations and significant contributions from 2D transport at the hetero-interface. Films grown with III/V ratio of 1.2 and Mg concentrations exceeding 2 × 1020 cm−3 show no detectable inversion domains or Mg precipitation. Highly Mg-doped p-GaN and p-AlGaN with Al fractions up to 27% similarly exhibit hole concentrations exceeding 2 × 1019 cm−3. The p-GaN and p-Al0.11Ga0.89N films show broad ultraviolet (UV) photoluminescence peaks, which intercept the valence band, supporting the presence of a Mg acceptor band. Finally, a multi-quantum-well light-emitting diode (LED) and p-i-n diode are grown, both of which demonstrate rectifying behavior with turn-on voltages of 3–3.5 V and series resistances of 6–10 Ω without the need for any post-metallization annealing. The LED exhibits violet-blue luminescence at 425 nm, while the p-i-n diode shows UV luminescence at 381 nm, and both devices still show substantial light emission even when submerged in liquid nitrogen at 77 K.

The surface morphology, microstructural, and optical properties of indium gallium nitride (InGaN) films grown by plasma-assisted molecular beam epitaxy under low growth temperatures and slightly nitrogen-rich growth conditions are studied. The single-phase InGaN films exhibit improved defect density, an absence of stacking faults, efficient In incorporation, enhanced optical properties, but a grainlike morphology. With increasing In content, we observe an increase in the degree of relaxation and a complete misfit strain relaxation through the formation of a uniform array of misfit dislocation at the InGaN/GaN interface for InGaN films with indium contents higher than 55-60%.

Indium gallium nitride (InGaN) alloys offer great potential for high-efficiency photovoltaics, yet theoretical promise has not been experimentally demonstrated. Several major challenges remain including polarization effects, suitable p-type doping, improved surface passivation, and growth of thick, high-quality InGaN layers. In this paper, we present numerical simulations of InGaN p-in single-junction solar cells to provide guidelines for performance improvement through optimization of device structures given achievable material characteristics. The performance of both InGaN/GaN heterojunction devices that are presently achievable and InGaN homojunction solar cells that should be feasible in the future are investigated through the calculation of characteristic parameters: short-circuit current density, open-circuit voltage, and conversion efficiency. These simulations study the effect of indium content, thickness, and background doping of the unintentionally-doped InGaN absorbing layer on the performance of both InGaN solar-cell designs. While the maximum efficiency of a p-in InGaN/GaN heterojunction solar cell with low indium composition is 11.3%, the conversion efficiency of heterojunction devices with high indium composition needed for longer wavelength absorption drastically reduces because of polarization effects. Above an indium composition of 45%, the modeled heterojunction devices do not operate as solar cells. Using presently achievable values of minority carrier lifetime and surface recombination velocity, the maximum efficiency of InGaN single-homojunction solar cells with optimized parameters is ~17%, which is significantly smaller than the theoretical maximum energy-conversion efficiency for singlejunction cells.

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The origin for high hole concentration in Mg‐doped GaN films grown by metal‐modulated epitaxy has been explored. We observe a Mg acceptor band characterized by a broad emission without phonon replicas and a high energy tail that overlaps with the valence band of GaN, giving rise to a reduced effective Mg activation energy. We attribute the high hole concentrations to the reduction of compensating nitrogen vacancy concentration and to effectively dispersed Mg atoms, which are incorporated into the lattice as single substitutional atoms. This has been achieved by a low temperature growth, a decrease in the III/V ratio, and a planar growth interface that results from the layer‐by‐layer approach using the metal‐modulated epitaxial technique.