This paper presents a comparative study of electron transport phenomena in n-type gallium nitride strongly doped, above the Mott transition, with silicon and germanium. The samples under study were grown by molecular beam epitaxy, metal-organic vapor phase epitaxy and halide vapor phase epitaxy. The temperature dependence of resistivity and Hall Effect was investigated at temperatures ranging from 10 K up to 650 K. The measurements at sub-room temperatures allow the study of scattering mechanisms related to extrinsic material properties. The observed temperature dependences of the electrical transport properties were analyzed in the frame of the model taking into account a typical scattering mechanism and degree of degeneracy of free carrier electron gas. The limitations of the applied models will be presented.

Exhaustive experimental study of aluminum incorporation in epitaxial 4H-SiC and 3C‑SiC films grown by chemical vapor deposition (CVD) was performed. The influence of polytype and substrate orientation was verified. Role of principal process conditions (growth temperature and pressure, deposition rate, chemical environment) was investigated in details. Finally, the evolution of optical properties of resulting SiC films with Al content was examined.

Zinc is often regarded as an alternative to magnesium p-type dopants in gallium nitride. However, besides many theoretical predictions, at present, there are poor data on experimentally revealed p-type conductivity and evaluation of Zn activation energy by means of electrical transport measurements. In this paper, ammonothermal crystallization of bulk GaN:Zn monocrystals is reported. Despite a high doping level of Zn (up to 2 × 10²⁰ cm⁻³), p-type conductivity with hole concentration as low as of 4 × 10¹⁵ cm⁻³ at room temperature and mobility about 3 cm²/V s was observed. A deep nature of the Zn acceptor was proved, as the ionization energy can exceed 260 meV. In addition, conduction in the impurity band appeared at temperatures as high as room temperature.

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled up with available Si atomic flux in a wide range of dopant concentrations. However, a surprisingly different behavior of the Ge dopant is observed, and the presence of atomically thin gallium or an indium layer dramatically affects Ge incorporation, hindering the fabrication of GaN:Ge structures with abrupt doping profiles. Here, we show an experimental study presenting a striking improvement in sharpness of the Ge doping profile obtained for indium as compared to the gallium surfactant layer during GaN-plasma-assisted molecular beam epitaxy. We show that the atomically thin indium surfactant layer promotes the incorporation of Ge in contrast to the gallium surfactant layer, which promotes segregation of Ge to the surface and Ge crystallite formation. Understanding the role of the surfactant is essential to control GaN doping and to obtain extremely high n-type doped III-nitride layers using Ge, because doping levels >10²⁰ cm⁻³ are not easily available with Si.

This paper discusses the results of high temperature resistivity and Hall effect studies of Mg-doped GaN and Al_xGa_1−xN epilayers (0.05 < x < 0.23). The studied samples were grown by molecular beam epitaxy on low temperature buffers of GaN and AlN deposited on a sapphire substrate. The experiments were carried out at temperatures ranging from 300 up to 1000 K. Up to a certain critical temperature T_C (around 800 K), a typical increase of the conduction processes due to the excitation of impurity states has been observed with an activation energy of about E_A = 200 meV. However, at this critical temperature T_C, an annealing effect was observed in all the investigated samples. At this critical temperature, the increase in the free carrier concentration as a function of time leads to an irreversible decrease in the samples’ resistivity of more than 60%. The observed temperature dependences of the electrical transport properties are analyzed in the frame of an impurity model including shallow donors and Mg-related acceptors (with E_A ∼ 200 meV). In some cases, an additional conduction channel not related to free carriers in the valence band must be taken into account. This can lead to an incorrect determination of hole concentration in the valence band, an important parameter in the process of radiative recombination.