Volume 87, Issue 3, 01 February 2000
Index of content:
- DEVICE PHYSICS (PACS 85)
Emitter-base bias dependence of the collector current ideality factor in abrupt AlGaAs/GaAs heterojunction bipolar transistors87(2000); http://dx.doi.org/10.1063/1.372036View Description Hide Description
Starting with the 4×4 Luttinger–Kohn Hamiltonian and making use of the axial approximation, we calculate the emitter current as a function of the applied forward emitter-base bias for a typical AlGaAs/GaAs single heterojunction bipolar transistor (HBT). While including the effects of emitter series resistance and recombination in the quasi-neutral base and emitter-base space-charge region, we then calculate the collector current density versus emitter to base bias and find it to be in excellent agreement with the experimental results for a HBT recently reported in the literature. For that structure, the collector current ideality factor is found to increase from 1.1 at low forward bias to 3.0 at large applied emitter-base forward bias approaching the built-in potential. Experimental values are equal to 1.2 and 2.25 at low and large respectively.
Nonlinear characteristics of magnetooptic Bragg diffraction in bismuth substituted yttrium iron garnet films87(2000); http://dx.doi.org/10.1063/1.372037View Description Hide Description
In this article, the nonlinear characteristics of magnetostatic forward volume wave (MSFVW)-based guided-wave magnetooptic Bragg cell modulators in bismuth-substituted yttriumiron garnet-gadolinium gallium garnet waveguides using nonuniform bias magnetic field are reported. First, the dispersion characteristics of the MSFVW under nonuniform bias magnetic field are analyzed, and the explicit expression for its bandwidth is determined. The transmission measurements of the MSFVW show that owing to the nonuniform magnetic field, the bandwidth is significantly increased. Next, the results of noncollinear magnetooptic (MO) Bragg diffraction experiments using the MSFVW in the frequency range from 2.0 to 4.0 GHz are presented. Two types of nonlinear process, namely, the four-magnon decay and modulation instabilities, are observed. However, the MO experiments at the carrier frequency of 2.85, 3.10, and 3.25 GHz suggest that the decay instabilities did not play a significant role in the MO interaction because of the larger degree of phase mismatch induced by the satellite waves generated during the nonlinear processes. We find that despite the presence of the decay instabilities, the MO Bragg diffraction characteristics still comply with that predicted by the coupled-mode theory before the nonlinear processes evolve into the modulation instabilities. Once the four-magnon modulation instabilities set in at the threshold powers, the MO Bragg diffraction will incur a drop in diffraction efficiency by as much as 9%. This feature results from perturbation of the satellite waves of smaller wave numbers induced in the modulation instabilities that lead to the MO phase mismatch. A model is established to describe the combined contributions of the initial MSFVW and the excited satellite waves associated with the modulation instabilities to the MO Bragg diffraction characteristics.
87(2000); http://dx.doi.org/10.1063/1.372038View Description Hide Description
Hysteresis was observed with nonequilibrium characteristics in the sidegate voltage dependence of drain current when measuring the threshold behavior of sidegating effect in GaAs metal–semiconductor field-effect transistors in the voltage-controlled condition. Once the sidegate voltage is varied in a quasi-steady state, hysteresis disappears immediately. A new mechanism is presented to explain the phenomenon that hysteresis are related to electron capture and emission from EL2 deep center on the substrate side of channel-substrate junction.
87(2000); http://dx.doi.org/10.1063/1.372039View Description Hide Description
The scanning capacitance microscope (SCM) is a carrier-sensitive imaging tool based upon the well-known scanning-probe microscope (SPM). As reported in Edwards et al. [Appl. Phys. Lett. 72, 698 (1998)], scanning capacitancespectroscopy (SCS) is a new data-taking method employing an SCM. SCS produces a two-dimensional map of the electrical junctions in a Si device and also provides an estimate of the depletion width. In this article, we report a series of microelectronics applications of SCS in which we image submicron transistors, Si bipolar transistors, and shallow-trench isolation structures. We describe two failure-analysis applications involving submicron transistors and shallow-trench isolation. We show a process-development application in which SCS provides microscopic evidence of the physical origins of the narrow-emitter effect in Si bipolar transistors. We image the depletion width in a Si bipolar transistor to explain an electric field-induced hot-carrier reliability failure. We show two sample geometries that can be used to examine different device properties.
87(2000); http://dx.doi.org/10.1063/1.372040View Description Hide Description
Self-assembledquantum dots(QDs) of highly strained InAlAs have been grown by molecular beam epitaxy in separate-confinement heterostructures on (001) GaAs substrates. Results from a systematic study of samples with varying amounts of deposited material relates the observed emission peaks with QD levels, wetting layer states, or barrier materials. For samples with high-QD concentration, lasing is observed in the upper-QD shells. A sample with contact layers improving carrier and optical confinement operates up to room temperature and displays lowered threshold current densities. A threshold current density of ∼4 A/cm2 is measured for this structure at and continuous-wave operation is obtained up to A material gain larger than is measured for this single-layer structure. Lasing is observed in the upper-QD shells for small gain media, and progresses towards the QD lower states for longer cavity lengths representing an emission shift of 45 meV. A minor dependence of the threshold on QD density is found for samples having densities between 20 and hundreds of QDs per micron squared. For samples with multiple QD layers displaying vertical self-assembling, an increase in the emission linewidth is observed compared with single-layer samples and multilayer samples with uncorrelated growth.