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Fabrication of low resistivity ohmic contacts to N polarity gallium nitride crystal is an important issue for the construction of the vertical current flow devices like laser diodes and high brightness light emitting diodes. Gallium nitride is a challenging material because of the high metal work function required to form a barrier-free metal-semiconductor interface. In practice, all useful ohmic contacts to GaN are based on the tunneling effect. Efficient tunneling requires high doping of the material. The most challenging task is to fabricate high quality metal ohmic contacts on the substrate because the doping control is here much more difficult that in the case of epitaxial layers. In the present work we propose a method for fabricating low resistivity ohmic contacts on N-side of GaN wafers grown by hydride vapor phase epitaxy. These crystals were characterized by a n-type conductivity and the electron concentration of the order of 1017 cm-3. The standard Ti-Au contact turned out to be unsatisfactory with respect to its linearity and resistance. Instead we decided to deposit high-n type ZnO layers (thickness 50 nm and 100 nm) prepared by atomic layer deposition at temperature of 200 °C. The layers were highly n-type conductive with the electron concentration in the order of 1020 cm-3. Afterwards, the metal contact to ZnO was formed by depositing Ti and Au. The electrical characterization of such a contact showed very good linearity and as low resistance as 1.6 × 10-3 ­Ω cm2. The results indicate advantageous properties of contacts formed by the combination of the atomic layer deposition and hydride vapor phase epitaxy technology. [ABSTRACT FROM AUTHOR]

p+-n GaN diodes were studied by means of conventional deep level transient spectroscopy and Laplace transform deep-level spectroscopy methods within the temperature range of 77-350 K. Deep level transient signal spectra revealed the presence of a majority and minority trap of indistinguishable signatures. The Laplace transform deep-level spectroscopy technique due to its superior resolution allows us to unambiguously identify and characterize the traps. The apparent activation energy and capture cross-section for the majority trap were found to be equal to 0.63 eV and 2 × 10-16 cm2 and for the minority trap 0.66 eV and 1.6 × 10-15 cm2. It has been confirmed that the Laplace transform deep-level spectroscopy technique is a powerful tool in characterization of the traps of close signatures. [ABSTRACT FROM AUTHOR]

Two samples containing InGaN quantum wells have been grown by metal-organic vapor phase epitaxy on high pressure grown monocrystalline GaN (0001). Different growth temperatures have been used to grow the wells and the barriers. In one of the samples, a low temperature GaN layer (730 ±C) has been grown on every quantum well before rising the temperature to standard values (900 ±C). The samples have been investigated by transmission electron microscopy and X-ray diffraction. Photoluminescence spectra have been measured as well. The influence of the LT-GaN has been investigated in regard to its influence on the structural and compositional quality of the sample. [ABSTRACT FROM AUTHOR]