Publications

Characterization of Shallow, Undoped Ge/SiGe Quantum Wells Commercially Grown on 8-in. (100) Si Wafers

Hutchins-Delgado, Troy A.; Miller, Andrew J.; Scott, Robin S.; Lu, Ping L.; Luhman, Dwight R.; Lu, Tzu-Ming L.

Hole spins in Ge quantum wells have shown success in both spintronic and quantum applications, thereby increasing the demand for high-quality material. We performed material analysis and device characterization of commercially grown shallow and undoped Ge/SiGe quantum well heterostructures on 8-in. (100) Si wafers. Material analysis reveals the high crystalline quality, sharp interfaces, and uniformity of the material. We demonstrate a high mobility (1.7 × 10⁵ cm² V^–1 s^–1) 2D hole gas in a device with a conduction threshold density of 9.2 × 10¹⁰ cm^–2. We study the use of surface preparation as a tool to control barrier thickness, density, mobility, and interface trap density. We report interface trap densities of 6 × 10¹² eV^–1. Our results validate the material’s high quality and show that further investigation into improving device performance is needed. We conclude that surface preparations which include weak Ge etchants, such as dilute H₂O₂, can be used for postgrowth control of quantum well depth in Ge-rich SiGe while still providing a relatively smooth oxide–semiconductor interface. Our results show that interface state density is mostly independent of our surface preparations, thereby implying that a Si cap layer is not necessary for device performance. Transport in our devices is instead limited by the quantum well depth. Commercially sourced Ge/SiGe, such as studied here, will provide accessibility for future investigations.