Mg-doping and free-hole properties of hot-wall MOCVD GaN
Alexis Papamichail, Anelia Kakanakova, Einar O. Sveinbjörnsson, Axel R. Persson, Björn Hult, Niklas Rorsman, Vallery Stanishev, Son Phuong Le, Per O. Å. Persson… 展开作者
Alexis Papamichail, Anelia Kakanakova, Einar O. Sveinbjörnsson, Axel R. Persson, Björn Hult, Niklas Rorsman, Vallery Stanishev, Son Phuong Le, Per O. Å. Persson, Muhammad Nawaz, Jr-Tai Chen, Plamen P. Paskov, Vanya Darakchieva
The hot-wall metal-organic chemical vapor deposition (MOCVD), previously shown to enable superior III-nitride material quality and high performance devices, has been explored for Mg doping of GaN. We have investigated the Mg incorporation in a wide doping range ($2.45\times{10}^{18}~cm^{-3}$ up to $1.10\times{10}^{20}~cm^{-3}$) and demonstrate GaN:Mg with low background impurity concentrations under optimized growth conditions. Dopant and impurity levels are discussed in view of Ga supersaturation which provides a unified concept to explain the complexity of growth conditions impact on Mg acceptor incorporation and compensation. The results are analysed in relation to the extended defects, revealed by scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and surface morphology, and in correlation with the electrical properties obtained by Hall effect and capacitance-voltage (C-V) measurements. This allows to establish a comprehensive picture of GaN:Mg growth by hot-wall MOCVD providing guidance for growth parameters optimization depending on the targeted application. We show that substantially lower H concentration as compared to Mg acceptors can be achieved in GaN:Mg without any in-situ or post-growth annealing resulting in p-type conductivity in as-grown material. State-of-the-art $p$-GaN layers with a low-resistivity and a high free-hole density (0.77 $Ω$.cm and $8.4\times{10}^{17}~cm^{-3}$, respectively) are obtained after post-growth annealing demonstrating the viability of hot-wall MOCVD for growth of power electronic device structures.
Ammonia (NH3) is commonly used as group V precursor in gallium nitride (GaN) metalorganic chemical vapor deposition (MOCVD). The high background carbon (C) impurity in MOCVD GaN is related to the low pyrolysis efficiency of NH3, which represents one of the fundamental challenges hindering the development of high purity thick GaN for vertical high power device applications. This work uses a laser-assisted MOCVD (LA-MOCVD) growth technique to address the high-C issue in MOCVD GaN. Carbon dioxide (CO2) laser with wavelength of 9.219 um was utilized to facilitate NH3 decomposition via resonant vib…
High-reflectance group III-nitride distributed Bragg reflectors (DBRs) were deposited by MOCVD on Si (111) substrates. A reflectance greater than 96% was demonstrated for the first time for an AlN/GaN DBR with a stop-band centered in the blue-green range of the visible spectrum. Crack-free GaN cap layers were grown on the DBR structures to demonstrate the opportunity to build III-nitride optoelectronic devices in this material. The DBR structure was under significant strain due to growth on a mismatched substrate although the GaN cap layer was shown to be strain free.
The reliability of AlGaN/GaN HEMTs adopting Fe and C co-doping, with high and low carbon doping concentration was investigated by means of different stress tests. Firstly, DC and pulsed I-V characterization at room temperature are discussed, then drain step stress tests at different gate voltages are compared, afterwards, the constant stress at different bias points are discussed. Results show that the high C HEMTs showed reduced DIBL, smaller leakage current, as well as decreased electric field, leading to an improved robustness during on-state stress testing, with respect to the reference on…
We present a novel p-GaN gate HEMT structure with reduced hole concentration near the Schottky interface by doping engineering in MOCVD, which aims at lowering the electric field across the gate. By employing an additional unintentionally doped GaN layer, the gate leakage current is suppressed and the gate breakdown voltage is boosted from 10.6 to 14.6 V with negligible influence on the threshold voltage and on-resistance. Time-dependent gate breakdown measurements reveal that the maximum gate drive voltage increases from 6.2 to 10.6 V for a 10-year lifetime with a 1% gate failure rate. This m…
For the development of reliable vertical GaN transistors, a detailed analysis of the robustness of the gate stack is necessary, as a function of the process parameters and material properties. To this aim, we report a detailed analysis of breakdown performance of planar GaN-on-Si MOS capacitors. The analysis is carried out on capacitors processed on different GaN bulk doping (6E18 Si/cc, 6E17 Si/cc and 2.5E18 Mg/cc, p-type), different structures (planar, trench-like) and different geometries (area, perimeter and shape). We demonstrate that (i) capacitors on p-GaN have better breakdown performa…
The direct integration of GaN with Si can boost great potential for low-cost, large-scale, and high-power device applications. However, it is still challengeable to directly grow GaN on Si without using thick strain relief buffer layers due to their large lattice and thermal-expansion-coefficient mismatches. In this work, a GaN/Si heterointerface without any buffer layer is successfully fabricated at room temperature via surface activated bonding (SAB). The residual stress states and interfacial microstructures of GaN/Si heterostructures were systematically investigated through micro-Raman spe…
The degradation mechanisms of AlGaN/GaN HEMTs adopting Fe and C co-doping, with high and low carbon doping concentration were investigated by means of hot-electron step stress and 24 hours stress tests. Firstly, DC and EL characterization at room temperature are summarized, then the parametric evolution during hot-electron step stress tests at the semi-on state was compared, the assumption for the degradation mechanism is that hot-electrons activated the pre-existing traps in the buffer, attenuate the electric field in the gate drain access region and damaging the gate contact, the parametric …
Investigation of nitrogen polar p-type doped GaN/AlxGa(1-x)N superlattices for applications in wide-bandgap p-type field effect transistors
本论文研究了N极性调制掺杂p-AlGaN/GAN超晶格的MOCVD生长及其电学性质。空穴层电荷密度和迁移率作为SL中的p型掺杂剂Mg的浓度和SL周期数的函数进行了研究。进行室温霍尔测量以确定空穴迁移率和薄层电荷密度。当空穴密度随着SL周期数的增加而增加时，空穴迁移率基本上不受影响，对于Mg调制掺杂为7.5e18 cm-3的N极性SL，在同时具有6.5e13 cm-2的高空穴密度时，空穴迁移率高达18 cm 2/Vs。对于可比较的均匀掺杂的Ga极性SL样品，测量到11 cm 2/Vs的迁移率。还报道了GAN/AlGaN材料系统的最低薄层电阻为5 kOhm/sq。测试结构的晶体管也被制造来研究这些SL结构的适用性，其中平面器件导致5 mA/mm的电流，并且FinFET结构导致超过100 mA/mm的电流。
