Abnormal Rectifying Characteristics of a Mg Doped GaN Schottky Diode

Abstract

Electrical properties of Ti/Al Schottky junctions formed on p-GaN layers are investigated using Hall, I-V and C-V measurements in the temperature range of 82∼500K. All data exhibit extremely strong low temperature carrier freeze out effects, assured by huge decreases of the Hall concentration, zero-bias capacitance and also diode current level as the temperature decreases below ∼150K. The dramatic decrease of current level at the low temperature range indicates that tunneling plays a more important role for the low temperature conduction and the junction shows ohmic-like I-V characteristics due to large series resistance. The barrier height estimated with the thermionic model varies with a strong temperature dependency from 1.21eV at 500K to 0.24eV at 82K. High frequency equivalent circuit analysis indicates that the corrected capacitance still shows a strong frequency dependency even after compensating the series resistance effect due to the slow response of Mg acceptor state. The transition frequency of the acceptor state, which is proportional to the emission rate of the deep level, is estimated to be 142KHz at room temperature. Low frequency C-V measurements provide a proper doping profile, revealing the ∼15nm thin layer with a high doping spike of ∼8×10¹⁸/cm³ near the sample surface and the constantly doped bulk layer with a doping level of ∼10¹⁷/cm³.