The Optoelectronic Characteristics of Schottky Barrier Diodes to Nonpolar A-plane GaN With R-plane Sapphire
| Autor: | Sheng-chieh Chen, 陳勝傑 |
|---|---|
| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 The study of the subject was characteristics of Schottky contact and Schottky photodetector of A-plane undoped GaN. We adopt the sample which was deposited A-plane GaN film on R-plane Al2O3 substrate. Different metal contacts including Pt, Cr, Ni and Ti were evaporated on undoped-GaN layer to serve as Schottky barrier. The Schottky barrier heights of the Pt, Cr, Ni, and Ti on undoped A-plane GaN were 0.88eV, 0.81eV, 0.69eV, and 0.68eV, respectively. And the S parameter of the A-plane GaN Schottky contact was 0.156. We found that the Schottky contact of A-plane GaN had a strong surface pining effect compared with Schottky contact of C-plane GaN. The leakage current at -4V of the Pt, Cr, Ni, and Ti on undoped A-plane GaN were 8.36x10-7A, 1.71x10-6A, 4.18x10-5A, and 7.171x10-5A, respectively. The significant leakage current might be from the high density defects such as pits, threading dislocations, of the A-plane GaN on R-plane Al2O3. The existence of the high density defects could cause the leakage path of the carriers and the Fermi-level pinning effect at the metal/semiconductor interface, revealing a weak dependence of Schottky barrier height. In order to reduce the leakage current effectively for the application of the photodetectors, we selected the LT-GaN or SiO2 to serve as inserting layer in between Ni and A-plane GaN interface. The reverse leakage current at -4V of Au/Ni/A-plane GaN Schottky diode was reduced to 2.79x10-7A by introducing the 30nm-thick LT-GaN inserting layer and could be further suppressed to 2.90x10-10A by using the 10nm-thick SiO2 inserting layer. However, the rejection ratio (355nm/400nm) of the Au/Ni/SiO2/A-palne GaN Schottky photodiode is about one more order better than the Au/Ni/LT-GaN/A-plane GaN Schottky photodiode.The experimental results displayed the SiO2 inserting layer in between the Ni and A-plane GaN interface could effectively reduce the leakage current and elevate the optical property. Because the A-plane GaN was suffered by anisotropic strain, it had the optical polarization anisotropy characteristics of light absorption. We find the modification of anisotropic strain can also effect the polarization sensitive. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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