We study the effect of different deposition conditions on the properties of In-polar InN grown by plasma-assisted molecular beam epitaxy. GaN buffer layers grown in the Ga-droplet regime prior to the InN deposition significantly improved the surface morphology of InN films grown with excess In flux. Using this approach, In-polar InN films have been realized with room temperature electron mobilities as high as 2250cm2∕Vs. We correlate electron concentrations in our InN films with the unintentionally incorporated impurities, oxygen and hydrogen. A surface electron accumulation layer of 5.11×1013cm−2 is measured for In-polar InN. Analysis of optical absorption data provides a band gap energy of ∼0.65eV for the thickest InN films.

The authors demonstrate the impact of growth kinetics on the surface and structural properties of N-face InN grown by molecular beam epitaxy. Superior surface morphology with step-flow growth features is achieved consistently under In-rich conditions in a low-temperature region of 500–540°C. Remarkably, off-axis x-ray rocking curve (ω scans) widths are found to be independent of the growth conditions. The band gap determined from optical absorption measurements of optimized InN is 0.651eV, while photoluminescence peak emission occurs at even lower energies of ∼0.626eV. Hall measurements show room temperature peak electron mobilities as high as 2370cm2∕Vs at a carrier concentration in the low 1017cm−3 region. Analysis of the thickness dependence of the carrier concentration demonstrates a n-type surface accumulation layer with a sheet carrier concentration of ∼3×1013cm−2.

The authors report on the excitation wavelength dependence of terahertz emission from n-InN and bulk p-InAs pumped with femtosecond pulses tunable from 800 to 1500 nm. The terahertz amplitude, normalized to pump and probe power, from both narrow band gap semiconductors remains relatively constant over the excitation wavelength range. In addition, terahertz radiation from In-and N-face InN samples with bulk carrier concentrations ranging from 10 17 to 10 19 cm −3is also investigated, showing a strong dependence of terahertz emission on bulk carrier concentration. The experimental results agree well with calculations based on drift-diffusion equations incorporating momentum conservation and relaxation.

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The effects of negative polarization charge at the n-InGaN∕p-GaN interface on the performance of hydride vapor phase-epitaxy deposited single heterostructure n-InGaN∕p-GaN LEDs with p-side down are investigated. The strong peak emission wavelength blueshift and concomitant superlinear increase in light output as the injection current increases below 25A∕cm2 are characteristic of radiative tunneling. We show that the combination of two-dimensional hole gas formation on the n-InGaN side of the heterointerface and enhancement of the electron barrier to transport across this interface results in only ∼10% efficiency droop up to 500A∕cm2 without implementation of an AlGaN electron-blocking layer or a second heterointerface.