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.
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 ...
The first study of photo-assisted anodic etching of unintentionally doped n-GaN at room temperature is reported here. The electrolyte used is a mixture of buffered aqueous solution of tartaric acid and ethylene glycol.The etching rate varies from -20 A/mm to as high as 1600 A/mm. A systematic study shows that (I) the etch rate, as well as the surface roughness, increases with the current density; (ii) the etching rate is the highest when the pH of the electrolyte is -7; and (iii) the etching is faster when there is more ethylene glycol in the electrolyte solution.
Indium droplet formation during the epitaxial growth of InxGa~_xN films is a serious problem for achieving high quality films with high indium mole fraction. In this paper, we studied the formation of indium droplets on the InxGal_ N films grown by metalorganic chemical vapor deposition (MOCVD) using single crystal x-ray diffraction. It is found that the indium (101) peak in the x-ray diffraction spectra can be utilized as a quantitative measure to determine the amounts of indium droplets on the film. It is shown by monitoring the indium diffraction peak that the density of indium droplets increases at lower growth temperature. To suppress these indium droplets, a modulation growth technique is used. Indium droplet formation in the modulation growth is investigated and it is revealed in our study that the indium droplets problem has been partially relieved by the modulation growth technique.
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