SILICON SILICON-GERMANIUM MULTIPLE-QUANTUM WELLS GROWN BY GAS-SOURCE MOLECULAR-BEAM EPITAXY - HYDROGEN COVERAGE AND INTERFACIAL ABRUPTNESS/

We have grown silicon-germanium/silicon (Si1-xGex/Si, x < 0.30) multip le quantum wells (MQWs) by gas-source molecular beam epitaxy (GSMBE) u sing disilane (Si2H6) and germane (GeH4) as source gases, and have cha racterized their structural properties by secondary ion mass spectrosc opy (SIMS), X-ray diffraction (XRD) rocking curve and transmission ele ctron microscopy (TEM) techniques. A substrate temperature of 520 degr ees C was maintained during growth resulting in a Si and SiGe growth r ate-limited primarily by hydrogen desorption kinetics. Under these con ditions, surface hydrogen is expected to function as a surfactant ther eby enhancing interfacial abruptness at the Si/SiGe interface through suppression of Ge surface segregation. Independent of Ge composition i n the Si1-xGex wells, we find abrupt interfaces, as determined from XR D measurements, and sharp SIMS decay lengths of the order of 2.5 nm/de cade. For nominally identical Si barriers in all samples examined, we find thicker barriers for the structures with higher Ge content in the well. For the specimens with x = 0.30 in the wells, we find a noticea ble well plus barrier period variation of approximately 5%-10% as dete rmined from XRD rocking curves, as well as TEM evidence for the onset of strain relaxation via interface undulation formation in the first q uantum well of the structure. A discussion of these results in terms o f hydrogen desorption kinetics is presented.