Metal contact formation to GaN based on the interface control technologies

本研究的目的是开发一个稳定的肖特基接触和欧姆接触与GaN的低电阻率的形成过程，基于GaN表面和金属-GaN界面的系统表征。主要研究结果如下：（1）采用X射线光电子能谱（XPS）对不同表面处理后的GaN表面进行了表征。在空气暴露的GaN表面发现了1.4 eV的强向上能带弯曲。这是由于表面态的高密度。在NH_4OH溶液和ECR激发的N_2等离子体中的表面处理显著地将表面能带弯曲减小到0.5eV，表明费米能级钉扎的减少。(2)我们通过详细的电流-电压-温度（I-V-T）测量研究了金属/n-GaN界面的漏电机制。在反向I-V曲线中观察到一个大的偏离电子发射（TE）输运， ...更多信息 rge过量泄漏。提出了一种基于近表面固定变化或表面态存在的势垒修正的场致发射（TFE）模型来解释所观察到的大反向漏电流。(3)提出了一种新的AlGaN/GaN异质结表面钝化工艺，即在GaN衬底上覆盖一层Al_2O_3（约1 nm）。在Al_2O_3钝化的异质结表面上的肖特基栅接触的反向漏电流比常规肖特基栅结构的反向漏电流降低了三个数量级。C-V测试结果表明，该新型栅极结构具有良好的二维电子气（2DEG）可控性。(4)Mg掺杂的GaN表面的XPS进行了表征。Mg掺杂GaN的表面Mg的积累似乎导致包括tenacionus氧化物层的无序表面层的形成，导致在表面处的1.3-1.4 eV的大的向下带弯曲。在ECR-N2等离子体中进行表面处理对去除这种无序层是非常有效的。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