Control of ion content and nitrogen species using a mixed chemistry plasma for GaN grown at extremely high growth rates >9 μm/h by plasma-assisted molecular beam epitaxy
Control of ion content and nitrogen species using a mixed chemistry plasma for GaN grown at extremely high growth rates >9 μm/h by plasma-assisted molecular beam epitaxy
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DOI：
10.1063/1.4933278
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发表时间：
2015-10-21
影响因子：
3.2
通讯作者：
Bresnahan, Rich C.
中科院分区：
文献类型：
--
作者：
Gunning, Brendan P.;Clinton, Evan A.;Bresnahan, Rich C.
利用改进的氮等离子体源，等离子体辅助分子束外延（PAMBE）已被用来实现更高的GaN生长速率。更高的传导性孔板，结合更高的氮气流量和增加的泵送能力，导致使用34 sccm的N-2时生长速率显著增加至8.4 μ m/h，同时仍保持可接受的低操作压力。进一步发现，可将氩加入等离子体气体中以提高生长速率至9.8 μ m/h，这是在600 W射频功率下使用20 sccm的N-2和7.7sccm的Ar流实现的，对于整个2英寸，厚度的标准偏差仅为2%。直径晶片。采用通量计的远程朗缪尔式探针用于间接测量等离子体中的相对离子含量。在低等离子体压力下使用氩气稀释导致等离子体离子电流急剧减少一半以上，而高等离子体压力抑制离子含量而不管等离子体气体化学。此外，不同的趋势是明显的分子和原子的氮物种产生的压力和氮组成的等离子体。氩气稀释导致几乎一个数量级的可实现的生长速率范围从1 μ m/h到近10 μ m/h。即使在超过6 μ m/h的膜生长，表面形态保持光滑，显示出清晰的原子步骤，均方根粗糙度小于1纳米。由于Si的低蒸气压，探索Ge作为用于高生长速率应用的替代n型掺杂剂。使用Ge掺杂在GaN中实现了2.2 x 10（16）到3.8 x 10（19）cm（-3）的电子浓度，并且无意掺杂的GaN膜表现出仅1-2 x 10（15）cm（-3）的低背景电子浓度。最高的生长速率导致由于Ga单元分裂的宏观表面特征，这是仍有待解决的工程挑战。尽管如此，显着提高的生长速率表明，PAMBE生长的III族氮化物器件的未来前景广阔。(C)2015 AIP Publishing LLC.
Utilizing a modified nitrogen plasma source, plasma assisted molecular beam epitaxy (PAMBE) has been used to achieve higher growth rates in GaN. A higher conductance aperture plate, combined with higher nitrogen flow and added pumping capacity, resulted in dramatically increased growth rates up to 8.4 mu m/h using 34 sccm of N-2 while still maintaining acceptably low operating pressure. It was further discovered that argon could be added to the plasma gas to enhance growth rates up to 9.8 mu m/h, which was achieved using 20 sccm of N-2 and 7.7 sccm Ar flows at 600 W radio frequency power, for which the standard deviation of thickness was just 2% over a full 2 in. diameter wafer. A remote Langmuir style probe employing the flux gauge was used to indirectly measure the relative ion content in the plasma. The use of argon dilution at low plasma pressures resulted in a dramatic reduction of the plasma ion current by more than half, while high plasma pressures suppressed ion content regardless of plasma gas chemistry. Moreover, different trends are apparent for the molecular and atomic nitrogen species generated by varying pressure and nitrogen composition in the plasma. Argon dilution resulted in nearly an order of magnitude achievable growth rate range from 1 mu m/h to nearly 10 mu m/h. Even for films grown at more than 6 mu m/h, the surface morphology remained smooth showing clear atomic steps with root mean square roughness less than 1 nm. Due to the low vapor pressure of Si, Ge was explored as an alternative n-type dopant for high growth rate applications. Electron concentrations from 2.2 x 10(16) to 3.8 x 10(19) cm(-3) were achieved in GaN using Ge doping, and unintentionally doped GaN films exhibited low background electron concentrations of just 1-2 x 10(15) cm(-3). The highest growth rates resulted in macroscopic surface features due to Ga cell spitting, which is an engineering challenge still to be addressed. Nonetheless, the dramatically enhanced growth rates demonstrate great promise for the future of III-nitride devices grown by PAMBE. (C) 2015 AIP Publishing LLC.