Fabrication of magnesium-doped gallium nitride nanorods and microphotoluminescence characteristicsKinetics of low-temperature activation of acceptors in magnesium-doped gallium nitride epilayers grown by metal-organic vapor-phase epitaxy Electrical characteristics of lateral p ϩ n diodes made from gallium nitride epitaxial layers on sapphire substrates are reported. The current-voltage characteristics are observed to have several distinct regions in which a tunneling current has been identified at low forward bias in addition to the conventional temperature-dependent diffusion current observed at moderate forward bias. A tunneling behavior indicates the presence of deep-level traps at the junction, which alter the electrical behavior of these junctions compared to the conventional behavior. In addition, space-charge-limited currents are found to influence these junctions at large forward and reverse bias.

Hexagonal boron nitride (hBN) growth was carried out on (111) Si substrates at a temperature of 1350 C using a cold wall chemical vapor deposition system. The hBN phase of the deposited films was identified by the characteristic Raman peak at 1370 cm À1 with a full width at half maximum of 25 cm À1 , corresponding to the in-plane stretch of B and N atoms. Chemical bonding states and composition of the hBN films were analyzed by X-ray photoelectron spectroscopy; the extracted B/ N ratio was 1.03:1, which is 1:1 within the experimental error. The fabricated metal-hBN-metal devices demonstrate a strong deep UV (DUV) response. Further, the hBN growth on the vertical (111) surfaces of parallel trenches fabricated in (110) Si was explored to achieve a thermal neutron detector. These results demonstrate that hBN-based detectors represent a promising approach towards the development of DUV photodetectors and efficient solid-state thermal neutron detectors.

We have applied frequency-dependent capacitance measurements and admittance spectroscopy on GaN:Mg to study the electronic states associated with Mg doping. Metalorganic vapor phase epitaxy GaN:Mg samples with two different Mg doping levels were grown and thermally annealed in nitrogen. Lateral dot-and-ring Schottky diodes using Au/Ti were fabricated. Frequency-dependent measurements on these diodes show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high-frequency modulation. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of one impurity-related acceptor level in the higher Mg-doped sample with an activation energy of 136 meV. For the lower Mg-doped sample, two acceptor levels at 124 and 160 meV were observed. We believe these levels are most probably associated with the Mg acceptor state itself, possessing energy levels which are very close to the results previously reported in the literature. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01617-9͔The successful p-type doping in metalorganic vapor phase epitaxy ͑MOVPE͒ GaN using Mg has allowed the realization of blue light emitting p-n junction diodes. Treatments, such as electron-beam irradiation 1 or thermal annealing, 2 are usually required to activate the p-type conduction. Electrical characteristics of these Mg-related acceptors are, however, not well understood. The Mg acceptor binding energy has been reported to be 250 and ϳ160 meV from the donor-acceptor pair transition and from temperature-dependent photoluminescence ͑PL͒ experiments, respectively.3 The temperature-dependent Hall measurements revealed a Mg-related activation energy of 157 meV. 4 In this letter, we report the electrical characterization of GaN:Mg, using frequency-dependent capacitance measurements and admittance spectroscopy, in order to study the electronic states associated with Mg doping. It is well known that deep traps greatly affect the free carrier profiles, as determined by capacitance-voltage (C -V) measurements. 5Given the aforementioned energy level depths associated with Mg, as well as the fact that Mg-doping is responsible for most or all of the observed p-type conductivity, the small signal capacitance of Mg-doped GaN is expected to be dependent on measurement frequency. We had also found that deep level transient spectroscopy ͑DLTS͒ could not be successfully used to characterize these Mg-related deep levels, principally due to the low diode capacitance level at low measurement temperatures. In contrast, admittance spectroscopy is better suited for the study of these relatively shallow and/or fast levels. Mg-doped GaN samples were grown in a horizontal MOVPE reactor at 100 Torr using trimethyl gallium ͑TMGa͒, bis-cyclopentadienyl magnesium ͑Cp 2 Mg), and ammonia (NH 3 ) on ͑0001͒ sapphire substrates.7 The Mgdoped layer, ϳ2 m in thickness, was grown at 1050°C at a growth rate of ϳ2 m/h. Two ...

A two-step process for synthesizing stable Cs 2 SnI 6 perovskite thin films is reported in this letter. The two-step process includes the co-evaporation of two precursors SnI 2 and CsI onto a glass substrate, followed by a post thermal annealing process in iodine vapor. Using this technique, pure Cs 2 SnI 6 perovskite thin films were successfully synthesized without any wet process. These perovskite thin films are found to be stable under ambient conditions. They also show an electron mobility up to 509 cm 2 V −1 s −1 , which is higher than the mobilities of films prepared by solution processes reported in the literature. IMPACT STATEMENTA novel two-step dry process to synthesize phase-pure, air-stable Cs 2 SnI 6 perovskite thin film with higher electron mobility than that of the films prepared by the solution process.

In an effort to improve the silicon carbide (SiC) substrate surface, a new electrochemical mechanical polishing (ECMP) technique was developed. This work focused on the Si-terminated 4H-SiC (0001) substrates cut 8°off-axis toward <1120>. Hydrogen peroxide (H 2 O 2 ) and potassium nitrate (KNO 3 ) were used as the electrolytes while using colloidal silica slurry as the polishing medium for removal of the oxide. The current density during the polishing was varied from 10 µA/cm 2 to over 20 mA/cm 2 . Even though a high polishing rate can be achieved using high current density, the oxidation rate and the oxide removal rate need to be properly balanced to get a smooth surface after polishing. A two-step ECMP process was developed, which allows us to separately control the anodic oxidation and removal of formed oxide. The optimum surface can be achieved by properly controlling the anodic oxidation current as well as the polishing rate. At higher current flow (Ͼ20 mA/cm 2 ), the final surface was rough, whereas a smoother surface was obtained when the current density was in the vicinity of 1 mA/cm 2 . The surface morphology of the as-received wafer, fine diamond slurry (0.1 µm) polished wafer, and EMCP polished wafer were studied by high-resolution atomic force microscopy (AFM).