AlN/β-Ga_(2)O_(3)异质结电子输运机制

Electron transport mechanism in AlN/β-Ga_(2)O_(3)heterostructures

β-Ga_(2)O_(3)具有禁带宽度大、击穿电场强的优点,在射频及功率器件领域具有广阔的应用前景.β-Ga_(2)O_(3)(2¯01)晶面和AlN(0002)晶面较小的晶格失配和较大的导带阶表明二者具有结合为异质结并形成二维电子气(two-dimensional electron gas,2DEG)的理论基础,引起了众多研究者关注.本文利用AlN的表面态假设,通过求解薛定谔-泊松方程组计算了AlN/β-Ga_(2)O_(3)异质结导带形状和2DEG面密度,并将结果应用于玻尔兹曼输运理论,计算了离化杂质散射、界面粗糙散射、声学形变势散射、极性光学声子散射等主要散射机制限制的迁移率,评估了不同散射机制的相对重要性.结果表明,2DEG面密度随AlN厚度的增加而增加,当AlN厚度为6 nm,2DEG面密度可达1.0×10^(13)cm^(-2),室温迁移率为368.6 cm^(2)/(V·s).在T<184 K的中低温区域,界面粗糙散射是限制2DEG迁移率的主导散射机制,T>184 K的温度区间,极性光学声子散射是限制2DEG迁移率的主导散射机制.

Theβ-Ga_(2)O_(3)has received much attention in the field of power and radio frequency electronics,due to an ultrawide bandgap energy of~4.9 eV and a high breakdown field strength of~8 MV/cm(Poncéet al.2020 Phys.Rev.Res.2033102).The in-plane lattice mismatch of 2.4%between the(2¯01)plane ofβ-Ga_(2)O_(3)and the(0002)plane of wurtzite AlN is beneficial to the formation of an AlN/β-Ga_(2)O_(3)heterostructure(Sun et al.2017 Appl.Phys.Lett.111162105),which is a potential candidate forβ-Ga_(2)O_(3)-based high electron mobility transistors(HEMTs).In this study,the Schrödinger-Poisson equations are solved to calculate the AlN/β-Ga_(2)O_(3)conduction band profile and the two-dimensional electron gas(2DEG)sheet density,based on the supposition that the 2DEG originates from door-like surface states distributed evenly below the AlN conduction band.The main scattering mechanisms in AlN/β-Ga_(2)O_(3)heterostructures,i.e.the ionized impurity scattering,interface roughness scattering,acoustic deformation-potential scattering,and polar optical phonon scattering,are investigated by using the Boltzmann transport theory.Besides,the relative importance of different scattering mechanisms is evaluated.The results show that at room temperature,the 2DEG sheet density increases with the augment of AlN thickness,and reaches 1.0×10^(13)cm^(-2)at an AlN thickness of 6 nm.With the increase of the 2DEG sheet density,the ionized impurity scattering limited mobility increases,but other scattering mechanisms limited mobilities decrease.The interface roughness scattering dominates the mobility at low temperature and moderate temperature(T<148 K),and the polar optical phonon scattering dominates the mobility at temperatures above 148 K.The room-temperature mobility is 368.6 cm^(2)/(V·s)for the AlN/β-Ga_(2)O_(3)heterostructure with an AlN thickness of 6 nm.