Double-barrier GaN resonant tunneling diodes with AlGaN barriers were fabricated on bulk (0001) single-crystal GaN substrates. Layers were grown using molecular-beam epitaxy with a rf plasma nitrogen source. Single diodes of $6\mu \mathrm{m}$ diameter were prepared by inductively coupled plasma reactive ion etching. For many diodes clear negative differential resistance is observed around $2\mathrm{V}$ with peak currents around $10\mathrm{kA}∕{\mathrm{cm}}^2$ and a peak-to-valley ratio of about 2 at room temperature. Its observation does not depend on specific conditions of measurement; however, it slowly decays after each measurement. The mechanism behind this decay is investigated since it is obviously prohibiting the usage of GaN resonant tunneling diodes so far. It is shown not to be caused by catastrophic breakdown of the devices.

We report on the InGaN multiquantum laser diodes (LDs) made by rf plasma-assisted molecular beam epitaxy (PAMBE). The laser operation at 408nm is demonstrated at room temperature with pulsed current injections using 50ns pulses at 0.25% duty cycle. The threshold current density and voltage for the LDs with cleaved uncoated mirrors are 12kA∕cm2 (900mA) and 9V, respectively. High output power of 0.83W is obtained during pulse operation at 3.6A and 9.6V bias with the slope efficiency of 0.35W∕A. The laser structures are deposited on the high-pressure-grown low dislocation bulk GaN substrates taking full advantage of the adlayer enhanced lateral diffusion channel for adatoms below the dynamic metallic cover. Our devices compare very favorably to the early laser diodes fabricated using the metalorganic vapor phase epitaxy technique, providing evidence that the relatively low growth temperatures used in this process pose no intrinsic limitations on the quality of the blue optoelectronic components that can be fabricated using PAMBE.

The results on growth and magnetotransport characterization of $\mathrm{Al}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ heterostructures obtained by plasma assisted molecular beam epitaxy on dislocation-free (below $100{\mathrm{cm}}^{-2}$ ) GaN high pressure synthesized bulk substrates are presented. The record mobilities of the two dimensional electron gas (2DEG) exceeding $100000{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ at liquid helium temperature and $2500{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ at room temperature are reported. An analysis of the high field conductivity tensor components allowed us to discuss the main electron scattering mechanisms and to confirm unambiguously the 2DEG room temperature mobility values.

We report on optically pumped lasing at 500 nm on InGaN laser structures grown by plasma assisted molecular beam epitaxy. The InGaN laser structures were grown under group III-rich conditions on bulk (0001) GaN substrates. The influence of the nitrogen flux and growth temperature on the indium content of InGaN layers was studied. We demonstrate that at elevated growth temperatures, where appreciable dissociation rate for In-N bonds is observed, the indium content of InGaN layers increases with increasing nitrogen flux. We show that growth of InGaN at higher temperatures improves optical quality of InGaN quantum wells, which is crucial for green emitters. The influence of piezoelectric fields on the lasing wavelength is also discussed. In particular, the controversial issue of partial versus complete screening of built-in electric field at lasing conditions is examined, supporting the former case.