A cubic GaN p–n diode has been grown on n-type GaAs (001) substrates by plasma assisted molecular epitaxy. For p- and n-type doping, elemental Mg and Si beams have been used, respectively. The optical properties are characterized by photoluminescence at room temperature and 2 K. Current–voltage and capacitance–voltage measurements of the cubic GaN n+–p junction are performed at room temperature. The electroluminescence at 300 K is measured through a semitransparent Au contact. A peak emission at 3.2 eV with a full width at half maximum as narrow as 150 meV is observed, indicating that near-band edge transitions are the dominating recombination processes in our device. A linear increase of the electroluminescence intensity with increasing current density is measured.
P-type doping with Mg and n-type doping with Si of cubic GaN (c-GaN) epilayers is reported. Cubic GaN films are grown by rf-plasma assisted MBE on semi-insulating GaAs (001) substrates at a substrate temperature of 720°C. Elemental Mg and Si are evaporated from thermal effusions cells. Secondary ion mass spectroscopy (SIMS), low temperature photoluminescence (PL) and temperature dependent Hall-effect measurements are used to study the incorporation, optical and electrical properties. A Mg related shallow donor-acceptor transiton at 3.04 eV with an acceptor activation energy of E A = 0.230 eV is observed by low temperature PL. At Mg concentrations above 10 18 cm -3 the dominance of a broad blue band indicates that also in c-GaN Mg is incorporated at different lattice sites or forms complexes. Si-doped c-GaN epilayers are ntype with electron concentrations up to 5*10 19 cm -3 . The incorporation of Si follows exactly the vapor pressure curve of Si, indicating a sticking coefficient of 1 for Si in c-GaN. With increasing Si-concentration the intensity of the near-band luminescence continuously increases and broadens.
Successful p-type doping of cubic GaN epilayers by carbon using an e-beam evaporation source is reported. At room temperature Hall-effect measurements of the C-doped cubic GaN epilayer gave hole concentrations and hole mobilities as high as 6 Â 10 17 cm --3 and 200 cm 2 /Vs, respectively. The thermal activation energy of the C-acceptor is (215 AE 10) meV. Low temperature photoluminescence spectra show a new line appearing at 3.08 eV. The emission energy increases with increasing e-beam evaporation power. This 3.08 eV line is attributed to a C related donor acceptor (D 0 A 0 ) transition.
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