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We report a fabrication method for laterally confining the two-dimensional electrons in InAs/AlSb single quantum wells into artificially patterned conducting wires. The minimum wire width is demonstrated to be ∼30 nm, among the smallest reported to date. The confining potential is approximately square and abrupt, and that makes the electron’s spatial distribution in the transverse direction the same as the physical width of the wire. The conducting electrons have close proximity to the surface charges, thus there is always a reduction in the elastic mean free path when the wire width decreases. Despite the reduction in mean free path, we find that the phase coherence length is approximately 1 μm at 2.2 K, a factor of 30 larger than the minimum feature size.

Transmission spectra of GaSb have been obtained over a temperature range from 10 to 470 °C. Using this information, transmission thermometry is applied to obtain accurate measurements of sample temperature during molecular beam epitaxy growth on GaSb substrates. A GaSb surface reconstruction transition is determined as a function of Sb flux and substrate temperature, establishing a laboratory-independent temperature standard.

C-ion irradiation was performed in CoFe/PtMn and CoFe/IrMn systems with an applied field during irradiation to investigate the effects of the energy transfer between C ions and antiferromagnetic atoms (AF) on the exchange field Hex. The irradiated CoFe/PtMn samples showed reduced exchange fields and coercivity, which was attributed to the lattice distortion of PtMn. When samples were irradiated with an applied field antiparallel to the original exchange-bias direction, a partially reversed Hex was found in CoFe/PtMn, while a fully reversed Hex in CoFe/IrMn was observed at the dose of 2×1014 ions/cm2. Rapid energy transfer and temperature increase, originating from the interaction between C ions and AF atoms, resulted in spin reversal and formation of reversed AF domains when samples were irradiated in antiparallel fields. In addition, the thermal relaxation of Hex in CoFe/IrMn was suppressed by ion irradiation.

To improve beam quality, an injection‐seeded unstable resonator was applied to a discharge‐pumped F2 laser, which is normally dominated by amplified spontaneous emission with a large beam divergence when using a normal stable cavity, due to the laser’s extremely high gain (a small‐signal gain‐length product ∼29). The time‐dependent injection‐seeding efficiency was obtained for various injection timings by measuring a ratio of the output laser intensity with the same polarization as the seed laser. Correlation of the injection‐seeding efficiency with the temporal evolution of the laser‐beam divergence was also studied. Both the time‐dependent beam divergence and the injection‐seeding efficiency showed degradation at a later part of the laser pulse.

We have investigated magneto‐transport and cyclotron resonance (CR) of two‐dimensional electron gas in silicon δ‐doped p‐InSb under a magnetic field of up to 12 T at 4.2 K. Because there are multiple subbands occupied, Shubnikov–de Haas oscillations show a beating behavior. The CR spectra also display several peaks originating from different subbands. Effective masses of electrons associated with the lowest three subbands can therefore be directly determined, and they are in excellent agreement with a self‐consistent calculation, which takes into account the electrostatic Poisson equation, the Schrodinger equation, and realistic sample parameters. Furthermore, we observed an absorption peak, whose resonance position has anomalous angle dependence. It is attributed to impurity CR where donors are in the vicinity of the δ‐doped sheet.

Infrared photoluminescence has been used to study the band-gap energy of InAs1−xSbx digital superlattices and band alignment of InAs1−xSbx/AlSb quantum wells at 5 K. It is found that the InAs1−xSbx digital alloys have a smaller effective band gap than InAs1−xSbx random alloys. In addition, the valence band offset between type-II InAs/AlSb is determined to be 130 meV. This number reduces as the Sb mole fraction in InAs1−xSbx is increased, and the alignment between InAs1−xSbx/AlSb becomes type I when x>0.15.

We report a calculation on the current‐voltage characteristics of double‐barrier resonant tunneling diodes. The results can well‐explain experimental observations, in particular, the temperature dependence of both the absolute current amplitude and the resonant voltage positions. Our calculation takes into account the self‐consistent Poisson equation, quantum mechanical tunneling, and band‐gap offset at the heterojunctions. In addition, the calculation includes a realistic scattering‐induced broadening effect, with which a quantitative fit throughout the entire negative differential resistance (NDR) region is demonstrated. Finally, we show that the differential resistance in the NDR region can be tuned, when asymmetrical tunneling barriers are used.

We present quantum mechanical self‐consistent calculations on the transfer characteristics of a new resonant tunneling transistor. The model structure consists of a source, a tunneling barrier, a quantum‐well drain, a thick insulator, and a backgate. The tunneling barrier consists of a double‐barrier structure. We demonstrate that based on energy and momentum conservations, the transistors display oscillatory negative transconductance, as the gate can control the resonant tunneling probability between source and drain. With the inclusion of a realistic energy relaxation time of ∼0.1 ps, the double‐barrier resonant tunneling transistor shows an enhancement of the tunneling current density and the negative transconductance feature is only slightly changed. We also find that the quantum‐well drain is not able to completely screen the electric field imposed by the backgate bias as a result of limited density of states of two‐dimensional systems.

We show that for narrow band‐gap semiconductors, the doping concentration deduced from capacitance‐voltage measurements can be substantially underestimated due to surface quantization effect. While our derivation can be applied to all materials, detailed accounts on p‐type Hg0.788Cd0.212Te are given as an example. We found that for a practical doping range, 1×1015 cm−3 to 1×1017 cm−3, the doping level can be underestimated by 53% to 173%, respectively.

We report experimental observation on the area and temperature dependence of the hysteresis in the current‐voltage characteristics of double‐barrier resonant tunneling diodes. Our observation shows that the hysteresis can simply result from a load line effect, since (1) the hysteresis will disappear when the the device area is reduced, and (2) the hysteresis becomes wider at lower temperatures. We compare the data with theoretical predictions from the intrinsic bistability picture, and obtain the criterion for observing current bistability.

We investigated the current‐voltage characteristics of double‐barrier resonant tunneling diodes with areas ranged from ∼400 μm2 to ∼10 μm2 at a temperature of 300 and 4.2 K. For diodes of large areas, the characteristic negative differential resistance is always accompanied by a hysteresis and oscillation at several tens of MHz. However, for smaller diodes, the hysteresis and oscillation disappear, and the tunneling current shows a smooth transition between peak and valley. Our observation shows that the hysteresis can result from a load line effect. Were the hysteresis an intrinsic behavior, it should persist as the device area is reduced. We therefore conclude that the intrinsic bistability is yet to be experimentally confirmed.

Our micromagnetic calculation demonstrates that the dominant coercivity mechanism is self-pinning in most exchange-coupled permanent and composite magnets. Such a pinning is attributed to the change of the intrinsic parameters associated with the phase change at the interface. From this self-pinning some more specific formulas on pinning field can be derived. In particular, for sufficiently large soft grains/defects, the pinning field can be expressed as HP=αHK, where HK=2k∕MS is the anisotropy field and α depends on the material parameters and micromagnetic structures. For an exchange-coupled Nd2Fe14B–αFe system with abrupt change of parameters in the interface, α≈0.1. Reducing the size of the soft grain will increase the coercivity, while the smooth change of the parameters in the interface will lead to a reduction in the coercivity. Comparison with experimental data justifies our calculation.

We propose and demonstrate an enhancement-mode AlxGa1−xAs∕GaAs single heterojunction field-effect transistor, in which the gate dielectric consists of an epitaxial AlxGa1−xAs layer and spin-on benzocyclobutene. The as-grown sample is undoped and, as a result, nonconductive at 4.2K. However, under a positive gate bias, high mobility two-dimensional electrons at the heterointerface are induced, as evidenced by magnetotransport characteristics. Numerical simulations of a model structure provide insight into applications in mesoscopic devices.

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance (MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 °C. The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR.

The stress relaxation behavior during thermal cycling of metal/quartz and metal/polyimide/quartz layered structures has been investigated using a cantilever bending beam technique. The metals chosen for this study include Cu and Cr, two materials with contrasting mechanical and interfacial bonding properties. A finite element analysis, as well as an analytical calculation, has been carried out to deduce the stress distribution in the layered structures. Results indicate that the extent of stress relaxation strongly depends on the intrinsic mechanical property of the metal film with significantly higher stresses residing in the Cr film than in the Cu film. The interfacial polyimide layer has been found to serve as an effective buffering layer to reduce the residual stress in metal films. Observations from transmission electron microscopy suggest that the stress is partially released through the deformation of the polyimide near the metal/polyimide interface.

Adhesion and interfacial failure of Cr, Cu, and Cu/Cr films on a thin pyromellitic dianhydride‐oxydianiline polyimide substrate have been investigated using a recently developed stretch deformation technique. This method directly measures the energy required to separate the interface from the difference in the load versus elongation curves between film/substrate and substrate structures. The failure mode was observed in combination with morphological studies by in situ optical microscopy and scanning and transmission electron microscopies. The stress distribution in the sample upon stretching has been computed by a finite element analysis. The difference in the stress relief modes, film fracture, and delamination behavior for Cu versus Cr films is discussed. The important role of crack formation in the metal overlayer for initiating failure is demonstrated. The effects due to the addition of a brittle Cr interface layer between polyimide and Cu on the buildup of stress and the onset of failure have also b...