Metal contact formation to GaN based on the interface control technologies

本研究的目的是在系统表征GaN表面和金属-GaN界面的基础上，开发稳定的肖特基接触和具有低电阻率的GaN欧姆接触的形成过程。得到的主要结果如下：(1)利用x射线光电子能谱（XPS）对不同表面处理后的氮化镓表面的化学和电子性质进行了表征。在空气暴露的GaN表面发现了1.4 eV的强向上弯曲带。这是由于表面态的高密度。在NH_4OH溶液和ecr激发的N_2等离子体中进行表面处理后，表面能带弯曲明显降低至0.5 eV，表明费米能级钉钉的降低。(2)通过详细的电流-电压-温度（I-V-T）测量，研究了金属/n-GaN界面的泄漏机制。在反向I-V曲线上观察到与热离子发射（TE）输运的较大偏差，并且有较大范围的过量泄漏。提出了一种新的基于近表面固定变化或表面状态的势垒修正热场发射（TFE）模型来解释观测到的大反向泄漏电流。(3)提出了一种利用超薄Al_2O_3层（~ 1 nm）对AlGaN/GaN异质结构进行表面钝化的新工艺。在al_2o_3钝化异质结构表面上，肖特基栅触点的反漏电流比传统肖特基栅触点的反漏电流减小了3个数量级。C-V结果表明，新型栅极结构具有良好的栅极可控性。(4)用XPS表征了掺杂mg的GaN表面。Mg在Mg掺杂GaN表面的积累似乎导致了包括氧化韧离子层在内的无序表面层的形成，导致了表面1.3-1.4 eV的大向下带弯曲。在ecr - n2等离子体中进行表面处理可以有效地去除这种无序层。少

The purpose of this research was to develop the formation processes of a stable Schottky contact and a ohmic contact with a low resistivity to GaN, based on the systematic characterization of the GaN surfaces and metal-GaN interfaces. The main results obtained are listed below:(1) Chemistry and electronic properties of GaN surfaces after various kinds of surface treatments were characterized by x-ray photoelectron spectroscopy (XPS). Strong upward band bending of 1.4 eV was found at the air-exposed GaN surface. This is due to the high density of surface state. The surface treatment in the NH_4OH solution and the ECR-excited N_2 plasma significantly decreased the surface band bending to 0.5 eV, indicating the reduction of the Fermi level pinning.(2) We investigated the leakage mechanism through metal/n-GaN interfaces by detailed current-voltage-temperature (I-V-T) measurements. A large deviation from the thermionic emission (TE) transport was observed in the reverse I-V curves with a la … More rge excess leakage. A novel barrier- modified thermionic-field emission (TFE) model based on presence of near-surface fixed changes or surface states was proposed to explain the observed large reverse leakage currents.(3) A novel surface passivation process for AlGaN/GaN heterostructures utilizing an ultrathin Al_2O_3 layer (〜 1 nm) was proposed. The reverse leakage current for the Schottky gate contact on the Al_2O_3-passivated heterostructure surface was reduced by three orders of magnitude than that for the conventional Schottky gate structure. C-V results showed good gate controllability two-dimensional electron gas (2DEG) by the novel gate structure.(4) Mg-doped GaN surfaces were characterized by XPS. The surface accumulation of Mg at the Mg-doped GaN seems to cause the formation of the disordered surface layer including a tenacionus oxide layer, leading to the large downward band-bending of 1.3-1.4 eV at the surface. The surface treatment in ECR-N_2 plasma was very effective in removing such a disordered layer. Less