Abnormal Rectifying Characteristics of a Mg Doped GaN Schottky Diode
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Abnormal rectifying characteristics of a Mg doped GaN Schottky diode Jae Wook Kim, Byung Kyu Cho, Jhang Woo Lee, and Phil W. Yu Department of Information and Communication, K-JIST, 1 Oryong-dong , Buk-gu, Gwangju, 500-712, Korea 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.. Introduction Electrical and optical characteristics of the p-type GaN or related materials have not been fully understood yet. Different from the n-type layer, the role of deep level states of Mg acceptors is not yet well defined and the conduction mechanism as well. The p-type Schottky junction has been investigated in an effort to understand the deep level influence on the conduction processes. However, only a few studies on this subject have been reported so far and even the barrier heights of various metal contacts are not likely well defined yet. For instance, the barrier height of the Ti/p-GaN junction varies from 0.65 to 2.3 eV, reportedly [1,2]. It is certain that the variation originates in part from the complex nature of semiconductor surface, and the various sample preparation methods are blamed sometime for the source of variation. This paper describes our effort to investigate the electrical conduction mechanism of the ptype GaN Schottky junction diode using the temperature dependent measurements of Hall concentrations, I-V and C-V characteristics. The Ti/Al metal junction was chosen for our experiment due to its low work function. The measurement temperature varied from 80K to 500K to fully disclose the temperature dependencies. To understand the specific role of Mg acceptors in dynamic properties C-V measurements were performed with a wide range of modulation frequency from 150Hz to 1MHz. Experiment 1µm-thi
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