Yanwu Lu

A model for scattering due to interface roughness in finite quantum wells

A model for scattering due to interface roughness in finite quantum wells (QWs) is developed within the framework of the Boltzmann transport equation and a simple and explicit expression between mobility limited by interface roughness scattering and barrier height is obtained. The main advantage of our model is that it does not involve complicated wavefunction calculations, and thus it is convenient for predicting the mobility in thin finite QWs. It is found that the mobility limited by interface roughness is one order of amplitude higher than the results derived by assuming an infinite barrier, for finite barrier height QWs where x = 0.3. The mobility first decreases and then flattens out as the barrier confinement increases. The experimental results may be explained with monolayers of asperity height 1-2, and a correlation length of about 33 angstrom. The calculation results are in excellent agreement with the experimental data from AlxGa1-xAs/GaAs QWs.

Surface roughness scattering in two dimensional electron gas channel

The mobility of AlxGa1−xN/GaN heterostructure two dimensional electron gas channel limited by surface roughness scattering was calculated considering the strong spontaneous and piezoelectric polarizations in III-group nitride heterostructure. The electronic mobility on the order of 104–105 cm2 V−1 s−1 was estimated. We found that the mobility limited by surface roughness scattering is very sensitive to barrier layer thickness fluctuation.

Polarization-induced remote interfacial charge scattering in Al2O3/AlGaN/GaN double heterojunction high electron mobility transistors

This study investigated on polarization-induced remote interfacial charge scattering, a scattering mechanism caused by the interfacial polarization charge, for Al2O3/AlGaN/GaN double heterojunction high electron mobility transistors (HEMTs). Results show that remote interfacial charge scattering plays a critical role in the mobility of two-dimensional electron gas (2DEG) in thin barrier HEMTs. The electronic mobility limited by remote charge scattering is found to be a function of the fixed charge density induced by the Al2O3 layer, 2DEG density, and barrier thickness. Results of this study can be used in designing structures to generate higher electron mobility in Al2O3/AlGaN/GaN double heterojunction HEMTs.

Converse piezoelectric effect induced misfit dislocation scattering in metal/AlGaN/GaN heterostructures

The converse piezoelectric effect on misfit dislocation (MD) generation and scattering in metal/AlGaN/GaN structures was quantitatively studied. The critical thickness of the structure decreased with increasing electric field in the growth direction and reached the maximum value at the zero field. The predicted MD density was in the order of 105 cm−1, which can be tuned by the gate voltage. The calculation result shows that MD scattering is a dominant limitation for electron mobility.

Binding Energy and Spin-Orbit Splitting of a Hydrogenic Donor Impurity in AlGaN/GaN Triangle-Shaped Potential Quantum Well

In the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling, the binding energyEband spin-orbit split energy Г of the ground state of a hydrogenic donor impurity in AlGaN/GaN triangle-shaped potential heterointerface are calculated. We find that with the electric field of the heterojunction increasing, (1) the effective width of quantum well decreases and (2) the binding energy increases monotonously, and in the mean time, (3) the spin-orbit split energy Г decreases drastically. (4) The maximum of Г is 1.22 meV when the electric field of heterointerface is 1 MV/cm.

Electric field-induced scatterings in rough quantum wells of AlGaN/GaN high-mobility electronic transistors

The electric field-induced surface and interface roughness scatterings have been investigated by taking both the forward and converse piezoelectric effects into account in AlGaN/GaN high electron mobility transistors. The results show that the converse piezoelectric effect can compensate the polarization fields in the barrier of AlGaN/GaN heterostructure, leading to weaker electric field scatterings. Additionally, the electronic mobilities limited by both surface and interface roughness can be modulated by the gate bias, based on which we can design the devices to obtain higher mobility.

Two-dimensional electron gas mobility limited by barrier and quantum well thickness fluctuations scattering in AlxGa1-xN/GaN multi-quantum wells

We calculate the electron mobility limited by the AlxGa1−xN barrier and the GaN well thickness fluctuations scattering of the two-dimensional electron gas (2DEG) at AlxGa1−xN/GaN multi-quantum wells (MQWs) with a triangle potential well. For this potential well, the ground subband energy is governed by the spontaneous and piezoelectric polarization fields and the fields are determined by the barrier and well thicknesses in undoped AlxGa1−xN/GaN MQWs. Thus, the thickness fluctuations of AlxGa1−xN barrier and GaN well will cause a local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.

Depolarization blueshift in intersubband transitions of triangular quantum wires

The depolarization effect (DE) in the intersubband transitions (ISBTs) of triangular cross-section quantum wires has been calculated in the framework of the effective-mass envelope-function theory and the self-consistent field approximation (Hartree approximation). Similar to quantum wells, the DE can bring an upward shift in ISBT. The shift quantities are affected significantly by apex angle but are insensitive to triangle size.

A Theoretical Calculation of the Impact of GaN Cap and

The electron mobility in a 2-D electron gas in a GaN/Al_xGa_1-xN/GaN heterostructure limited by GaN cap-thickness-fluctuation (CTF) and Al_xGa_1-xN barrier thickness-fluctuation (BTF) scattering is calculated considering the strong spontaneous and piezoelectric polarization. The calculated results reveal that the electron mobility limited by CTF and BTF scattering is lower than that limited by interface roughness scattering if the Al_xGa_1-xN barrier layer is thin enough (several nanometers).

\hbox{Al}_{x}\hbox{Ga}_{1-x}\hbox{N}

The electron mobility limited by spacer layer thickness fluctuation (SLTF) scattering on the two-dimensional electron gas in AlGaAs/GaAs modulation-doped heterostructure is investigated. Although the SLTF scattering and the interface roughness scattering are both induced by the roughness of the AlGaAs/GaAs interface, they are two different scattering mechanisms. The interface roughness will lead to the fluctuation of the distance from the electrons to the ideal interface and the fluctuation of the spacer layer thickness. The former induces the fluctuation of the electron potential, which works as the interface roughness scattering potential. The latter induces the fluctuation of the sheet carrier density in the channel, which causes a fluctuation in the quantization energy level. The quantization energy level fluctuation works as the SLTF scattering potential. Compared with the interface roughness scattering, the results reveal that the SLTF scattering becomes the dominant scattering mechanism when the do...