Studies of silicon germanium tunneling heterostructures grown by silicon molecular beam epitaxy

This study is to investigate some of the properties and their possible applications of SiGe tunneling devices. In order to calculate the band structures and band offsets of strained SiGe layers, deformation potential theory and a strain Hamiltonian have been employed based on strain tensors for different substrate orientations and alloy concentrations. The established band structures serve as a guideline for later experiments and the large valence band offset and small directional effective mass of the light hole suggest the convenience of development of SiGe heterostructure devices using valence band engineering.; Boron doping with simple filament heating was used in order to overcome conventional complicated boron cell structure and serious problems of Ga doping. SIMS measurement shows doping profile abruptness of about decade/200 A. Doping concentrations higher than 1 {dollar}times{dollar} 10{dollar}sp{lcub}20{rcub}{dollar} {dollar}cmsp{lcub}-3{rcub}{dollar} within 50 A layer have been achieved by this method.; Resonant tunneling diodes have been grown on various substrates. A tunneling diode grown on (100) relaxed Ge{dollar}sb{lcub}0.4{rcub}{dollar}Si{dollar}sb{lcub}0.6{rcub}{dollar} buffer layer shows 2.1 peak-to-valley current ratios at 4.2 K and 1.66 at 77 K. Three resonant peaks are observed by current-voltage I-V and the first and second derivatives. These agree with the calculated two heavy and light hole subband states in the quantum well. Even though injected carriers from the emitter are heavy holes, the major resonant peak is due to the light hole state in the well. A tunneling diode with a strained Ge{dollar}sb{lcub}0.25{rcub}{dollar}Si{dollar}sb{lcub}0.75{rcub}{dollar} well on Si substrate also shows a similar maximum peak-to-valley current ratio at 4.2 K. For this diode two resonance peaks are observed, through the heavy and the light hole ground states. Subband dispersion and transmission coefficient show a strong band mixing and thus tunneling through light hole subband is evident. Magnetotunneling measurements also confirm the heavy and light hole tunneling from a heavy hole input. The measured ratio of the heavy to light hole effective masses in the Ge{dollar}sb{lcub}0.4{rcub}{dollar}Si{dollar}sb{lcub}0.6{rcub}{dollar} quantum well is 3.9 compared with the theoretically estimated value of 2.8.; We extended our study of double barrier resonant tunneling to a three terminal device structure for studying hot carrier effects in SiGe heterostructure and possible device applications. A number of interesting features are evident in the I-V characteristics. In the current control mode, typical bipolar transistor-like current voltage characteristics are obtained. The injected carriers are near- ballistically transferred from the emitter to the collector. The device exhibits a controllable negative differential resistance in the current voltage characteristics.