High quality Ge layers for Ge/SiGe quantum well heterostructures using chemical vapor deposition

A great deal of interest is directed nowadays toward the development of innovative technologies in the field of quantum information and quantum computing, with emphasis on obtaining reliable qubits as building blocks. The realization of highly stable, controllable, and accessible hole spin qubits is strongly dependent on the quality of the materials hosting them. Ultraclean germanium/silicon-germanium heterostructures have been predicted and proven to be promising candidates and, due to their large scalability potential, they are opening the door toward the development of realistic and reliable solid state, all-electric, silicon-based quantum computers. In order to obtain ultraclean germanium/silicon-germanium heterostructures in a reverse grading approach, the understanding and control over the growth of Ge virtual substrates and thin films is key. Here we present a detailed study on the growth kinetics, morphology, and crystal quality of Ge thin films grown via chemical vapor deposition by investigating the effects of growth temperature, partial pressure of the precursor gas, and the use of Ar or ${\mathrm{H}}_{2}$ atmosphere. The presence of carrier gases catalyzes the deposition rate and induces a smoothening on the surfaces of films grown at low temperatures. We investigated the surface roughness and threading dislocation density as a function of deposition temperature, partial pressure, and gas mixture. Ge thin films deposited by diluting $\mathrm{Ge}{\mathrm{H}}_{4}$ in Ar or ${\mathrm{H}}_{2}$ were employed as virtual substrates for the growth of full Ge/SiGe quantum well heterostructures. Their defect density was analyzed and their electric transport properties were characterized via Hall measurements. Similar results were obtained for both carrier gases used.