AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS+EL-ThM

Paper SS+EL-ThM3
Encapsulation of SiGe Quantum Wells and Quantum Dots

Thursday, November 7, 2002, 9:00 am, Room C-110

Session: Structure of Semiconductor Surfaces & Interfaces
Presenter: G.G. Jernigan, US Naval Research Laboratory
Authors: G.G. Jernigan, US Naval Research Laboratory
P.E. Thompson, US Naval Research Laboratory
Correspondent: Click to Email
Semiconductor device characteristics are dependent on the chemical and structural properties of the electrical interface. As such, we are interested in SiGe quantum wells and quantum dots grown in Si. Heterojunctions between Si / SiGe / Si are chemically smeared due to Ge segregation, but little is known about the structural nature of the heterojunctions. We will present an STM study of the encapsulation of a Si@sub 0.8@Ge@sub 0.2@ alloy grown in Si at 500, 650, and 800 °C. Alloy deposition induces a rougher morphology than the inital Si surface. Intermixing of Ge from the alloy with the Si substrate is observed to happen immediately to produce a rough surface. The amount of intermixing increases with increasing growth temperature, and at 800 °C the surface roughness exceeds the thickness of deposited alloy. After intermixing, Ge segregates out from the alloy, and the surface Ge leads to an island growth mechanism, which further increases the surface roughness. At 500, 650, and 800 °C the alloy surfaces obtain a steady-state value for surface roughness, which has been characterized as 2D planar, rippled, and hutted, respectively. Encapsulation of the alloy layer with Si attempts to restore a smooth morphology. At 800 °C where the height of the huts are ~40 nm, a 5 nm Si layer reduced the hut height to ~10 nm, and after 20 nm of Si, the huts are gone. Remnants of the underlying alloy morphology can still be seen on the surface in the form of square pits where material did not fill in between the huts. For lower growth temperatures, less Si is needed to reduce the surface roughness, and square pits are still observed from the underlying alloy. The square pits arise from Ge segregation modifying the S@sub A@ and S@sub B@ step-edge sticking coefficient of Si to produce equal sized S@sub A@ and S@sub B@ terraces. A structural model for the heterointerfaces based on the STM observations will be presented.