Showing papers by "Mark S. Hybertsen published in 2003"

Transition structure at the Si(100)-SiO2 interface

Abstract: We characterize the transition structure at the Si(100)-SiO2 interface by addressing the inverse ion-scattering problem. We achieve sensitivity to Si displacements at the interface by carrying out ion-scattering measurements in the channeling geometry for varying ion energies. To interpret our experimental results, we generate realistic atomic-scale models using a first-principles approach and carry out ion-scattering simulations based on classical interatomic potentials. Silicon displacements larger than 0.09 Angstrom are found to propagate for three layers into the Si substrate, ruling out a transition structure with regularly ordered O bridges, as recently proposed.

A theoretical investigation of the characteristic temperature T/sub 0/ for semiconductor lasers

Abstract: The temperature dependence of the characteristic temperature T/sub 0/ of semiconductor quantum-well lasers is investigated using detailed simulations. The critical-temperature-dependent processes are the optical gain and the nonradiative recombination. The gain model is based on k /spl middot/ p theory with the multiple quantum wells in the active layer represented by a superlattice. The Auger process is assumed to be thermally activated. It is shown that, with inclusion of the continuum state filling and interband mixing, the most important features experimentally observed in the temperature dependence of the T/sub 0/ value can be explained. The continuum state filling and band nonparabolicity cause a significant deviation from the ideal linear carrier density versus temperature relation for quantum wells. The results are compared to experiment for broad area devices lasing at 980 nm and 1.3, and 1.55 /spl mu/m, and show good agreement over a broad range of temperature.

Microscopic simulation of the temperature dependence of static and dynamic 1.3-/spl mu/m multi-quantum-well laser performance

Abstract: The temperature dependence of the performance of 13-/spl mu/m Fabry-Perot (FP) multiple-quantum-well (MQW) lasers is analyzed using detailed microscopic simulations Both static and dynamic properties are extracted and compared to measurements Devices with different profiles of acceptor doping in the active region are studied The simulation takes into account microscopic carrier transport, quantum mechanical calculation of the optical and electronic quantum well properties, and the solution of the optical mode The temperature dependence of the Auger coefficients is found to be important and is represented by an activated form Excellent agreement between measurement and simulation is achieved as a function of both temperature and doping profile for static and dynamic properties of the lasers, threshold current density, and effective differential gain The simulations show that the static carrier density, and hence the contribution to the optical gain, varies significantly from the quantum wells on the p-side of the active layer to those on the n-side Furthermore, the modal differential gain and the carrier density modulation also vary Both effects are a consequence of the carrier dynamics involved in transport through the MQW active layer Despite the complexity of the dynamic response of the MQW laser, the resonance frequency is determined by an effective differential gain, which we show can be estimated by a gain-weighted average of the local differential gain in each well