| Co-Investigator(Kenkyū-buntansha) |
MORI Hidetsugu KYOTO UNIVERSITY,Graduate School of Engineering, Research Associate, 工学研究科, 助手 (60283644)
KOIDE Yasuo KYOTO UNIVERSITY,Graduate School of Engineering, Associate Prot., 工学研究科, 助教授 (70195650)
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| Research Abstract |
In order to examine the possibility of preparing an non-reacted(non-alloyed)ohmic contacts to p-GaN,the effects of GaN surface treatments and work functions of the contact metals on the electrical properties between the metal contacts and p-GaN were investigated. A contamination layr consisting of GaO_x and adsorbed carbons was found on the GaN substrate grown by metalorganic chemical vapor deposition. The contamination layr was not completely removed by sputtering the GaN surface with Ar and N ions where the ion densities were -10-^2 muA/cm^2. Although the contamination layr was partially removed by immersing in a buffered HF solution, little improvement of the electrical properties of the GaN/metal interfaces was obtained. Most of the vontamination layr was removed by annealing the Ni and Ta contacts at temperatures close to 500ﾟC.These annealed contacts exhibited slightly enhanced current injection from the contact metal to the GaN.The present surface treatment study indicated that
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removal of the contamination layr did not significantly reduce the contact resistance. On the other hand, the resistance decreased exponentially with increasing the metal work functions, where Pt, Ni, Pd, Au, Cu, Ti, Al, Ta, and Ni/Au were deposited on the GaN.This result suggests that the Schottky barrier height at the p-GaN/metal interface might not be pinned at the GaN surface. The present study concluded that a contact metal with a large work function is desirable for non-reacted ohmic contacts to p-GaN.However, these contacts did not provide the law contact resistance required for blue laser diodes.
In addition, Schottky barrier heights(SBH's)of a variety of metals(In, Cd, Nb, Ti, W,Cu, Ag, Au, Ni, Pt, and Se)contacting to p-ZnSe grown by a molecular beam epitaxy method were measured by an intenal photoemission, capacitance-voltage(C-V)、and/or current density-voltage(J-V)method. The internal photoemission method could not measure accurately the SBH's of these metals due to a strong interference of the monochromatic incident light in the p-ZnSe epilayr. The C-V method measured the SBH value of 1.23 eV for the Au contact and 1.13 eV for the Ni contact, but did not measure the SBH's of other metals due to strong hysteresis of the C-V curves. The SBH's of these metals were successfully measured by the J-V method to be 1.2(]SY.+-。[)0.1 eV.The present experiment showed that the SBH values were independent of the work functions of the contact metals, indicating that the Fermi-level could be pinned at the p-ZnSe/metal interface. In addition, turn-on voltages conventionally used to evaluate the electrical properties of the contact metals were found to be very sensitive to the SBH values. Less
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