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Professor,
Materials Science and Engineering,
Indian Institute of Technology-Kanpur ,
Work Phone: (512) 2597353,
Email: saboo[at]iitk.ac.in
Materials Science and Engineering,
Indian Institute of Technology-
Email: saboo[at]iitk.ac.in
Hare Krishna's Thesis
Thesis Topic:
Contacts on p-GaN and their characterization
Contacts on p-
GaN is a wide direct-bandgap semiconductor which has a broad range of potential applications in optoelectronic, high temperature and high power electronic devices. In order to enhance the performances of such devices, it is essential to develop thermal Instable and low resistance ohmic contacts on both n- and p-type GaN. In this regard, many investigations have been carried using different metal systems. However, it is difficult to obtain ohmic contacts, having low specific contact resistance, with p-type GaN because of the low activation of p-type dopants in GaN. Ni-Au metal system is the standard contact used for p-GaN, which provides the low specific contact resistance.
Ni-Au ohmic contacts were made on p-type GaN having 4.4 x 10 19cm-3 hole concentration. The specific contact resistance of a Ni/Au contact on p-GaN after oxygen anneal was determined on the order of 10 -1 Ωcm2, which is significantly higher than the best value (10-6 Ωcm2) reported in the literature. However, the basic current-voltage characteristics of the contact in determining the specific contact resistance are not significantly different. This lead us to a detailed evaluation of the CTLM technique for measuring the specific contact resistance. The analysis shows that in materials such as p- GaN, which is highly resistive, a low specific resistance may be difficult to measure by
standard transmission line methods below approximately 10-2 - 10-3 Ωcm2. This means reports using this technique to measure specific contact resistance on GaN below the .above value seem to be incorrect.
ε1-Cu 3Ge ohmic and schottky contacts were also made on p-GaN, since Cu-Ge alloy after
annealing produces a low resistivity si-Cu 3Ge phase which is also stable at high temperatures. Cu3Ge contact does not make an ohmic contact even after annealing at 400 and 500°C in vacuum, Ar and N2 for 30 minutes. We have also investigated this system as the schottky contact material for p-GaN. We get non-ideal I-V characteristics. The schottky barrier height is calculated using temperature dependent current voltage (I-V-T) techniques to be 0.66 eV. The ε-Cu 3Ge work function is measured using Kelvin probe to be 4.26 eV.
ε1-