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In the case of molecular beam epitaxy (MBE), the Mg acceptors are electrically active in the as‐grown material and a priori no additional annealing procedure is necessary. However, there are still some peculiarities in the electrical properties of ammonia‐process grown GaN:Mg and some annealing effect can be observed. Additionally, the character of weak temperature dependence in the vicinity of room temperature suggests that to describe the conduction process an additional conduction channel not related to the free carriers in the valence band must be taken into account. For these reasons, this article presents the results of low‐temperature resistivity and Hall Effect studies of Mg‐doped, ammonia‐process‐grown GaN. The studied samples are grown on low‐temperature buffers of GaN deposited on a sapphire substrate. High‐temperature annealing process (≈800 K) is carried out for all of them. The temperature dependences of the electrical transport properties before and after the annealing procedure are especially investigated at temperatures ranging from 10 up to 300 K. It is found that the low temperatures transport properties are sensitive to the annealing procedure and to describe the observed effects the hopping phenomena must be taken into account. [ABSTRACT FROM AUTHOR]

Inductively coupled plasma (ICP) is widely used in dry etching of III‐nitride materials, wherein the etching parameters of GaN and AlN are very different. Herein, the ICP dry etching process parameters of GaN/AlN periodically stacked structure (PSS) for avalanche photodiode (APD) fabrication are intensively studied and optimized. The flow rate ratio of Cl2/BCl3/Ar plasma, bias voltage, and the GaN‐to‐SiNx selectivity of ICP etching are optimized to achieve excellent surface morphology and nearly vertical sidewalls. It is found that the etching rate and the etched surface roughness of GaN/AlN material are significantly influenced by the flow rate of Cl2. After optimizing the etching procedure, the root‐mean‐square roughness of the etched surface is measured to be 1.46 nm, which is close to the as grown surface. By using the optimized ICP dry etching in the fabrication of the GaN/AlN PSS APD, the dark current is suppressed from 3.6 to 8.2 × 10−3 A cm−2 at −90 V. [ABSTRACT FROM AUTHOR]