Development of High Performance Ohmic Contact Materials for Full Color Light Enitting Devices.

为了探讨在p-GaN上制备非反应(非合金化)欧姆接触的可能性，研究了GaN表面处理和接触金属功函数对金属接触与p-GaN之间电学性质的影响。在金属有机化学气相沉积生长的GaN衬底上发现了由GaO_x和吸附碳组成的污染层。用离子密度为-10-2MUA/cm2的Ar和N离子溅射GaN表面并不能完全去除污染层。虽然在缓冲的HF溶液中浸泡可以部分去除污染层，但GaN/金属界面的电学性质几乎没有得到改善。通过在接近500ﾟC的温度下对Ni和Ta触头进行热处理，去除了大部分的Von污染层。这些退火的触头表现出从触点金属到GaN的电流注入略有增加。目前的表面处理研究表明，…更多地去除污染层并没有显著降低接触电阻。另一方面，随着金属功函数的增加，电阻呈指数下降，在GaN上沉积了铂、镍、钯、金、铜、钛、铝、Ta和Ni/Au。这一结果表明，p-GaN/金属界面的肖特基势垒高度可能不是钉扎在GaN表面的。本研究的结论是，对于p-GaN的非反应欧姆接触来说，具有大功函数的接触金属是可取的，但这些接触不能提供蓝色激光二极管所需的接触电阻。此外，通过内部光电子能谱、电容-电压(C-V)、和/或电流密度-电压(J-V)方法测量了用分子束外延方法生长的多种金属(In、Cd、Nb、Ti、W、Cu、Ag、Au、Ni、Pt和Se)与p-GaN接触的肖特基势垒高度。由于p-ZnSe外延层中单色入射光的强烈干扰，内光电子能谱方法不能准确测量这些金属的SBH。C-V法测量了Au接触的SBH值为1.23 eV，Ni接触的SBH值为1.13 eV，但由于C-V曲线的强烈滞后，没有测量其他金属的SBH值。用J-V法测得这些金属的SBH为1.2(]sy.+-)。[)0.1 eV。实验表明，SBH值与接触金属功函数无关，表明费米能级可以钉扎在p-ZnSe/金属界面上。此外，传统上用来评估触头金属电性能的开启电压对SBH值非常敏感。较少

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 … More 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