Atomic-Scale Insights into Semiconductor Heterostructures: From Experimental Three-Dimensional Analysis of the Interface to a Generalized Theory of Interfacial Roughness Scattering

Abstract

In this manuscript, we develop a generalized theory for the scattering process produced by interface roughness on charge carriers and which is suitable for any semiconductor heterostructure. By exploiting our experimental insights into the three-dimensional atomic landscape of Ge/GeSi heterointerfaces obtained by atom probe tomography, we have been able to define the full set of interface parameters relevant to the scattering potential, including both the in-plane and axial correlation inside real diffuse interfaces. Our experimental findings indicate a partial coherence of the interface roughness along the growth direction within the interfaces. We show that it is necessary to include this feature, previously neglected by theoretical models, when heterointerfaces characterized by finite interface widths are taken into consideration. To show the relevance of our generalized scattering model in the physics of semiconductor devices, we implemented it in a non-equilibrium Green's function simulation platform to assess the performance of a Ge/SiGe-based THz quantum cascade laser. § these authors contributed equally to this work

Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells

“…1c,d), STEM shows sharp and abrupt interfaces, with a broadening due to SiGe intermixing in the order of 0.8 nm [21]. The quality of the heterointerfaces is confirmed by the low value of the rootmean-square interface roughness which was estimated to be 0.18 nm by atomic probe tomography measurements performed on the same set of samples [30]. The thickness of wells and barriers reported in Table 1 was measured by energy-dispersive x-ray spectroscopy (EDX), while the periodicity of the MQW stack D SL was obtained by XRD.…”

Electron-phonon coupling in n -type Ge two-dimensional systems

“…Moreover, to accurately describe the scattering rate associated to IFR, selected samples have been investigated also by means of atom probe tomography 5 . In this way, we were able to precisely measure the root-mean square (rms) amplitude Δ (0.18 nm) and the in-plane correlation length Λ// (6.9 nm) associated to the interface roughness.…”

“…Due to a more mature epitaxy technology, carrier scattering in low dimensional systems has been investigated mainly focusing on III-V based structures 2,3 . However, in the last two decades, advances in group-IV epitaxy have made possible to grow SiGe multilayer systems with high crystal quality [4][5][6][7][8] ; consequently this class of materials is attracting increasing research efforts, mainly motivated by its prompt integrability with the mainstream CMOS standard. In particular, in the last ten years, SiGe Ge-rich structures have been actively investigated, and applications have been proposed in different contexts as for instance quantum computing [8][9][10] , Si-based photonics [11][12][13] , high mobility transistors 14,15 , and thermoelectricity 16,17 .…”

Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models

“…In the following, the ISB non-radiative lifetimes have been calculated from a full-subband population dynamics model [42] based on equations similar to those that lead to the results of Figure 3 but are adapted to the specific ACQW samples and consider the optical pumping conditions of the present work. In particular, to correctly account for inter-and intra-subband particle and energy fluxes in ACQWs, we included here, in addition to electron-phonon scattering, the contribution of the elastic scattering channels due to interface roughness (assuming an interface roughness amplitude of 0.2 nm with correlation length of 7.0 nm [12]) and to ionized impurity. In fact, the latter is expected to play a role at the high doping levels required for QFLs.…”

“…Since an electrically pumped Ge/SiGe QCL has been designed but not realized yet [9][10][11], optically pumped devices may offer an easier experimental test bench to assess the performances of models with out-of-equilibrium intersubband (ISB) population dynamics. For optically pumped lasers, electrical contacts are not required, thus eliminating most of the device processing steps and related difficulties [12], and besides, much simpler active layer QW stacks are needed compared to QCLs. The basic structure for an optically pumped QW emitter consists of two asymmetric (i.e., of different thickness and/or composition) wells coupled through a thin tunnelling barrier (asymmetric coupled QWs, ACQWs) [13].…”