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Notes: We have investigated in detail the influence of interlayer structures on nonalloyed ohmic contact resistance (ρc), in terms of the crystalline defects and the potential barrier at the interlayer/GaAs interface. The interlayer structures are a graded-band-gap InAs/GaAs strained-layer superlattice (graded SLS), a graded-band-gap InGaAs, and conventional SLSs without graded band gaps. A two-layer transmission line model indicates that the barrier resistance in the interlayer highly depends on the interlayer structure: ≤5×10−8 Ω cm2 for the graded SLS and graded InGaAs interlayers and 10−5–10−6 Ω cm2 for the conventional SLS interlayers. To explain the large dependence of the interlayer structure, first, the density and distribution of the misfit dislocations and stacking faults caused by the large lattice mismatch between InAs and GaAs have been investigated in detail by high-resolution transmission electron microscopy. In the graded SLS and conventional SLS interlayers, the influence of the high-density depletion regions spread near the crystalline defects is found to be negligible because of the high doping concentrations (∼1019 cm−3) in the interlayers. Second, the potential barrier at the interlayer/GaAs interface has been investigated by simulating the barrier resistance. The potential barrier profile is calculated self-consistently with Poisson's equation and the Schrödinger equation. Tunneling current through the barrier is analyzed using the Wentzel–Kramers–Brillouin approximation or the numerical wave solution to the Schrödinger equation. The graded SLS interlayer has the effectively smooth conduction band profile without the barriers, which is similar to that of the graded InGaAs interlayer, because of its short period SLS. In the conventional SLS interlayers, the reasonable barrier heights of 0.14–0.26 eV obtained by this simulation indicates that these barriers are the dominant factor which increases the contact resistances. For the low-resistance nonalloyed ohmic contact, therefore, a smooth conduction band profile without band discontinuity is more predominant than the reduction in the crystalline defect density.

Notes: GaAs selective epitaxial growth by molecular-beam epitaxy (MBE) was studied as a function of substrate temperature. Selectivity was observed at as low as 600 °C with 1×10−5 Torr As pressure and a 0.04 μm/h growth rate. The heterogeneous nucleation theory gives a good explanation for the selectivity dependence on substrate temperature. Selective epitaxial growth by MBE is promising for device applications which require thin localized epilayers.

Notes: Silicon dioxide films are sputter deposited on polycrystalline silicon (polysilicon) in an oxygen-argon atmosphere at 200 °C. Electrical conduction and breakdown are measured at various gate fields and temperatures. In addition to the Fowler–Nordheim tunneling current reported for thermal oxide, the sputter-deposited films have another, newly identified high-activation-energy current as electrical conduction mechanisms. The high-activation-energy current contribution to the total current is considerably reduced by increasing the oxygen mixing ratio and/or by decreasing the sputtering gas pressure, resulting in a considerable total current reduction. High-activation-energy current contributes little to the triggering of breakdown, unlike Fowler–Nordheim tunneling injections. In contrast to polysilicon thermal oxide, sputter-deposited films on polysilicon have no observable field enhancement in Fowler–Nordheim tunneling current, which indicates smooth surfaces. Thus, electrical properties in oxygen-argon sputter-deposited films on polysilicon are explained by high-activation-energy current and Fowler–Nordheim tunneling current.

Notes: Damage and contamination-free chemical dry etching of (100)GaAs and (100)InP by Cl2 was demonstrated using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy (MBE) system. This system consists of a combined etching chamber, an MBE chamber, and a sample preparation chamber, all at ultrahigh vacuum. A mirrorlike surface was obtained after etching at substrate temperatures ranging from 300 to 400 °C for GaAs, and from 200 to 400 °C for InP. In situ reflection high-energy electron diffraction observations were accomplished for GaAs, with a mirrorlike surface after etching, and (2×4) surface reconstruction was observed. Results show that a smooth surface was formed at an atomic level.

Notes: Characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs) with sputter-deposited gate-oxide films at 4.2 K under high magnetic fields of up to 10 T are presented. The gate-oxide films are deposited by oxygen-argon sputtering of an SiO2 target at 200 °C, much lower than a conventional thermal oxidation temperature of 1000 °C. The MOSFET using a sputter-deposited film has a Hall mobility of 7000 cm2/V s at 4.2 K. The quantum Hall effect and Shubnikov–de Haas oscillations are successfully observed. The magnetic angle dependence of the magnetoresistance and the Shubnikov–de Haas oscillation indicate that this MOSFET has a two-dimensional electron gas. Analysis of the perpendicular magnetoresistance and the quantum Hall effect indicates that this MOSFET has a weakly localized state similar to that of thermal oxide film.

Notes: The molecular-beam epitaxial growth conditions for (InAs)m(GaAs)n short period superlattices (SPSs) on GaAs substrates have been optimized by monitoring reflection high-energy electron diffraction (RHEED) intensity oscillations. The RHEED oscillation measurements enable understanding InAs growth behavior on a 7% lattice-mismatch GaAs substrate. Within one monolayer InAs deposition with lower than 560 °C growth temperature can give high SPS crystalline quality. The SPS periodic structure and the monolayer InAs formation, embedded in GaAs layers, have been confirmed by x-ray diffraction and transmission electron microscopy measurements. The obtained thickness controllability for the SPSs is less than±6% for InAs and ±3% for GaAs. The electron Hall mobilities for modulation-doped structures having an (InAs)1(GaAs)n SPS as an electron channel, whose layer index of n varied from 3 to 6, have been compared with those with a pseudomorphic InGaAs random alloy channel which has the equivalent In composition. The SPS channel samples have shown up to 15% higher electron Hall mobilities than the InGaAs alloy channel samples at 77 K. A 0.2-μm-gate (InAs)1(GaAs)6 superlattice channel modulation-doped field-effect transistor (FET) has exhibited a maximum extrinsic transconductance of as high as 450 mS/mm with a 70-GHz cut-off frequency at room temperature. The best noise figure of 0.58 dB with an associated gain of 11.15 dB has been attained. The obtained device characteristics are comparable or superior to those for the corresponding InGaAs alloy channel FETs. These results demonstrate, for the first time, the (InAs)m(GaAs)n SPS potentialities as an ordered counterpart for InGaAs random alloy for high-speed device applications.

Notes: Silicon dioxide films, 8–100 nm thick, are sputter deposited in an oxygen-argon atmosphere onto a silicon substrate at 200 °C. Electrical conduction and dielectric breakdown in oxygen-argon sputter-deposited film are measured using metal-oxide-semiconductor capacitors and compared with those in thermal dioxide film. Moreover, their mechanisms are investigated. Thin oxygen-argon sputter-deposited film is found to have the same low electrical conduction and high dielectric breakdown as thermal dioxide film. Electrical conduction through oxygen-argon sputter-deposited film shows small temperature dependence and Fowler–Nordheim characteristics. For a wide range of film thickness, the breakdown field in oxygen-argon sputter-deposited film correlates well with that in thermal dioxide film and with the impact ionization/recombination model. Thus, the electrical conduction mechanism through oxygen-argon sputter-deposited silicon dioxide film is Fowler–Nordheim tunneling, and dielectric breakdown is explained by the impact ionization/recombination model.

Notes: GaAs was selectively grown on GaAs substrates patterned with SiO2 by conventional molecular beam epitaxy (MBE). No growth was found on SiO2, except for small GaAs particles, when the substrate temperature was above 700 °C under 1.2×10−5 Torr arsenic pressure. With the increase in the substrate temperature, the selectivity was better while the growth rate decreased. At 775 °C, no growth occurred, even on GaAs. Selective epitaxial growth of GaAs by MBE is promising for application to device fabrications.

Notes: An In surface segregation effect during the growth of InGaAs on GaAs by molecular-beam epitaxy has been studied by reflection high-energy electron diffraction measurements supported by a segregation model. Indium atoms segregate at a ratio of more than 0.8 under the conventional growth conditions for InGaAs, which causes the formation of accumulated In atoms on the surface. The transition from two-dimensional to three-dimensional growth occurs when the amount of In reaches around 1.7 monolayer with a nominal alloy composition greater than 0.25. This transition determines the upper limit on the In composition of the InGaAs layer for application as an electron channel in modulation-doped field-effect transistors.