Anisotropic roughness scattering at a heterostructure interface

Applied Physics Letters, 1996

To explore the role of interface scattering in high electron mobility transistor ͑HEMT͒ device performance, a series of samples consisting of both a superlattice and a HEMT structure were grown by molecular beam epitaxy ͑MBE͒ at temperatures ranging from 500 to 630°C. Hall measurements indicate a trend toward higher mobilities in samples grown at higher temperatures. Subsequent x-ray reflectivity measurements were made, and the data were fitted by least-squares refinement of a calculated reflectivity curve determined from a model of the sample structure to obtain the composition profile along the growth direction. These results indicate smoother interfaces for the samples with higher mobilities.

Microelectronics Journal, 2003

Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy. The spectra at room temperature show Franz -Keldysh oscillations associated to the substrate -buffer layer interface. The built-in electric field magnitude calculated from these oscillations is related with the two-dimensional electron gas (2DEG) mobility. In addition we observed two signals associated to the GaAs capping layer and to the 2DEG, respectively. q

Applied Physics Letters, 2010

We demonstrate a method of making a very shallow, gateable, undoped 2-dimensional electron gas. We have developed a method of making very low resistivity contacts to these structures and systematically studied the evolution of the mobility as a function of the depth of the 2DEG (from 300nm to 30nm). We demonstrate a way of extracting quantitative information about the background impurity concentration in GaAs and AlGaAs, the interface roughness and the charge in the surface states from the data. This information is very useful from the perspective of molecular beam epitaxy (MBE) growth. It is difficult to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to have a large enough spacer layer to reduce scattering and switching noise from remote ionsied dopants.

Physical Review B

A theoretical model was formulated for electron scattering in a two-dimensional electron gas confined in a triangular potential well. For the first time, the effects of intersubband scattering were included. An inherent mobility limit is imposed by phonon, alloy, and remote impurity scattering. Intersubband scattering was found to play a significant role in determining this mobility limit. The model accounted very satisfactorily for the reported electron mobility characteristics in GaAs-GaA1As heterostructures. The two-dimensional electron gas confined at a GaA1As-GaAs interface has received a great deal of attention' 6 because its unique transport characteristics play a key role in a new generation of ultra-high-speed semiconductor devices. Thus, in "selectively doped" GaAlAs-GaAs heterostructures, electrons confined at the GaAs side of the interface and separated from their parent donors, which are in GaAlAs, have exhibited mobilities as high as 2& 10 cm'/Vs;~this value is about one order of magnitude greater

Semiconductor Science and Technology, 1990

Two MBE-grown GaAslAlGaAs heterostructure wafers have been modified by helium ion implantation. Since implantation essentially only changes electron mobility, our low-temperature experiments allowed us to study the quantum corrections to the electrical conductivity as a function of mobility.

Physica E-Low-Dimensional Systems & Nanostructures, 2003

We present a novel model to calculate vertical transport properties such as conductance and current in unintentionally disordered double-barrier GaAs-AlxGa1−xAs heterostructures. The source of disorder comes from interface roughness at the heterojunctions (lateral disorder) as well as spatial inhomogeneities of the Al mole fraction in the barriers (compositional disorder). Both lateral and compositional disorder break translational symmetry along the lateral direction and therefore electrons can be scattered o the growth direction. The model correctly describes channel mixing due to these elastic scattering events. In particular, for realistic degree of disorder, we have found that the e ects of compositional disorder on transport properties are negligible as compared to the e ects due to lateral disorder. ?

2001

Surface morphology of high mobility heterostructures is examined and correlated with d.c. transport. All samples examined show evidence of lines in the [110] direction with roughness ranging from small amplitude features to severe anisotropic ridges. Transport in these samples is consistent with that in samples having artificially induced 1D charge modulations. The native surface properties reflect a prevalent, anisotropic disorder affecting 2D electron conduction. Importantly, the native lines are orthogonal to the stripes theoretically proposed to explain high Landau level transport anisotropies.

Anisotropic transport properties of a two-dimensional electron gas in nonpolar m-plane AlN/GaN heterostructures with the interface roughness coupled anisotropic in-plane strain scattering were investigated theoretically using a path-integral framework. The scattering potential was composed of the interface roughness and the effective field from the electron charge and the net piezoelectric polarization. We showed that the anisotropic biaxial strains generate only the net piezoelectric polarization along the [0 0 0 1]-direction and cause anisotropy in electron mobility with a magnitude lower than the [1120] -direction. We also showed that the anisotropy in electron mobility reduced with increasing electron density. Moreover, the anisotropic electron mobility disappeared when the anisotropic in-plane strain scattering was removed, and the relation for pure interface roughness scattering was reestablished. This formulation with existing roughness parameters gave a good description for the experimental results of polar c-plane AlN/GaN heterostructures.

Physical Review B, 1990

Journal of the Korean Physical Society, 2020

We studied the properties of electron transport in mesoscopic GaAs/AlGaAs heterostructure without any intentional dopants in which an external electric field defined the two-dimensional electron gas (2DEG). An electrically formed 2DEG without intentional doping offers many advantages because of the absence of high concentrations of charged scattering centers. We demonstrate that the electron concentration can be easily tuned by varying the gate voltage. This tunability was observed for a high-quality 2DEG with a carrier density ranging from 0.75 to 3.34 × 10 11 cm −2 , for which the corresponding mobility ranged from 0.26 to 2.93 × 10 6 cm 2 V −1 s −1. The mobility of the 2DEG is closely followed the experimental power law for high-mobility wafers, μ ∝ n 0.7 2D .