Growth, structural, and electrical properties of germanium-on-silicon heterostructure by molecular beam epitaxy

Abstract

The growth, morphological, and electrical properties of thin-film Ge grown by molecular beam epitaxy on Si using a two-step growth process were investigated. High-resolution x-ray diffraction analysis demonstrated ∼0.10% tensile-strained Ge epilayer, owing to the thermal expansion coefficient mismatch between Ge and Si, and negligible epilayer lattice tilt. Micro-Raman spectroscopic analysis corroborated the strain-state of the Ge thin-film. Cross-sectional transmission electron microscopy revealed the formation of 90 ° Lomer dislocation network at Ge/Si heterointerface, suggesting the rapid and complete relaxation of Ge epilayer during growth. Atomic force micrographs exhibited smooth surface morphology with surface roughness < 2 nm. Temperature dependent Hall mobility measurements and the modelling thereof indicated that ionized impurity scattering limited carrier mobility in Ge layer. Capacitance- and conductance-voltage measurements were performed to determine the effect of epilayer dislocation density on interfacial defect states (Dit) and their energy distribution. Finally, extracted Dit values were benchmarked against published Dit data for Ge MOS devices, as a function of threading dislocation density within the Ge layer. The results obtained were comparable with Ge MOS devices integrated on Si via alternative buffer schemes. This comprehensive study of directly-grown epitaxial Ge-on-Si provides a pathway for the development of Ge-based electronic devices on Si.

Temperature and doping-dependent interplay between the direct and indirect optical response in buffer-mediated epitaxial germanium

“…Additionally, the 2× and 4× increase in bulk electron and hole mobilities compared to Si, as well as Ge's narrow bandgap, has fostered rapid progress toward realizing ultra-low power transistors using Ge. Motivated by the possibility of integrating Ge electronic devices with Si, as along with Ge-based light emission sources for communications, several approaches have been implemented to create a direct or quasi-direct bandgap Ge, namely: (i) tensile strained Ge as-deposited on Si [22] induced via thermal expansion coefficient mismatch; (ii) tin alloying with Ge [14,16,[23][24][25][26][27]; (iii) flexible Ge membranes [31][32][33]; and (iv), III-V compound semiconductor-based strain templates underneath the Ge layer [5,[34][35][36][37][38][39][40][41]. These methods have been shown to enhance the optical emission from Ge, wherein both electrically-and optically-pumped lasing from Ge [25][26][27][28][42][43][44] have been demonstrated.…”

Highly Tensile-Strained Self-Assembled Ge Quantum Dots on InP Substrates for Integrated Light Sources

“…The future TS-Ge-QD based lasers are expected to show superior performance over the current GeSn thin film or quantum well lasers, for the following reasons. First, as the active region, the TS-Ge-QDs can be grown at the optimal temperatures of Ge leading to very high crystalline quality with minimum point defects. , This is unlike GeSn that requires a low growth temperature in order to obtain high enough Sn concentration without segregation. Second, both TS-Ge-QD and GeSn have to be monolithically grown on strain-relaxed template layers with pre-existing defects.…”

Synthesis of Armchair Graphene Nanoribbons on Germanium-on-Silicon

“…Surface roughening of the Ge(001) surface during graphene nanoribbon synthesis has been previously reported 22 and can potentially affect the carrier mobility of nanoribbons on Ge by increasing surface scattering. 71 Therefore, we next study the impact of nanoribbon synthesis on the surface roughness of Ge/Si(001) and Ge(001). We find that the roughness depends on (1) the density of the nanoribbons and (2) the length of the nanoribbons.…”