Akihiro Shibatomi

Characterization of WSix/GaAs Schottky contacts

The Schottky diode characteristics of WSix contacts on n‐type GaAs have been investigated and correlated to the film stress in WSix and crystallographic properties of the film. Experimental results show that (1) the high‐temperature stability of WSix/GaAs Schottky diode characteristics depends significantly on Si content; (2) WSix/GaAs contacts exhibit very high‐temperature‐stable Schottky diode characteristics at Si content around 0.60, and at this Si content no metallurgical interactions between WSix and GaAs are observed by 2‐MeV 4He+ Rutherford backscattering (RBS) measurements; (3) the optimum Si content for Schottky diode characteristics coincides with that for stress minimum in WSix; (4) the Schottky diode characteristics are not affected by whether WSix is crystallized or not, and a common feature of the regions where the Schottky diode characteristics are very high‐temperature stable is that each consists of single‐phase (W5Si3 secondary solid solution or amorphous).

Residual Donors in High Purity Gallium Arsenide Epitaxially Grown from Vapor Phase

Residual impurities involved in a GaAs layer epitaxially grown from vapor phase are identified by far-infrared photoconductivity measurement. Silicon, selenium, sulfur and germanium are readily incorporated as shallow donors into GaAs epitaxial layers. The dominant residual donor is sulfur for epitaxial layers grown by Ga-AsCl3-N2 system and it is silicon or sulfur for epitaxial layers by usual Ga-AsCl3-H2 system. From spectral peaks of the photoconductivity in a magnetic field, the donor ionization energies for silicon, selenium, sulfur and germanium are estimated to be 5.759 meV, 5.812 meV, 5.845 meV and 5.949 meV respectively.

Effect of Thermal Etching on GaAs Substrate in Molecular Beam Epitaxy

Thermal etching of GaAs substrates prior to epitaxial growth by molecular beam epitaxy has been used to reduce carrier depletion at the substrate and epitaxial layer interface. The amount of carrier depletion between a Si-doped n-GaAs substrate and a Si-doped n-GaAs epitaxial film, measured by a C-V carrier profiling technique, was proved to decrease significantly with increased etched depth at a substrate temperature of 750°C. The origin of the carrier depletion is believed to be the carbon acceptor, from the results of C-V measurement and secondary ion mass spectrometory. Based on these results, thermal etching was successfully applied to semi-insulating GaAs substrates to improve mobility and sheet concentrations of two-dimensional electron gas in the selectively doped GaAs/N-Al0.3Ga0.7As heterostructures with very thin GaAs buffer layers (0.2 µm).

RESONANT-TUNNELING HOT ELECTRON TRANSISTOR (RHET)

Abstract This paper reviews our current activities in hot electron transistors, and then describes recent advances in the RHET technology using InGaAs-based materials. The RHETs emitter common current gain is typically 10 to 17, with a maximum of 25, which is about four times greater than that of a GaAs-based RHET. The collector current peak-to-valley ratio reaches 19.3, with a maximum of 21.7, eight times that of the GaAs-based RHET. These are followed by theoretical and experimental analyses of the RHETs DC performance. It is found that theoretical and experimental results do not agree for the GaAs-based RHET but agree well for the InGaAs-based RHET.

Orientation effect of self‐aligned source/drain planar GaAs Schottky barrier field‐effect transistors

The effect of orientation on self‐aligned source/drain planar GaAs Schottky barrier field‐effect transistors (FET’s) has been investigated. The dependence of the threshold voltage of FET’s on gate length was measured for FET’s oriented in two perpendicular [110] directions. Both stress‐enhanced lateral spread of implanted ions and lateral diffusion at the gate material/GaAs interface are proposed as possible mechanism to account for the orientation effect. The experiments indicate that the preferred direction for the self‐aligned FET fabrication on a (100) substrate is [011].

Influence of carbon and oxygen on donor formation at 700 °C in Czochralski‐grown silicon

Influence of oxygen and carbon on donor formation by annealing at 700 °C was studied by infrared absorption, resistivity, and spreading resistance measurements in Czochralski‐grown silicon. Donor concentration correlates with both oxygen and carbon reductions by the annealing at 700 °C. Donor distribution corresponds to etch pit distribution observed after the annealing. The donor is proposed to be oxygen precipitate nucleated at carbon site. The influence of the donor generation on the device parameter in metal‐oxide‐ silicon memory field‐effect transistors is discussed.

A resonant-tunneling bipolar transistor (RBT)―a new functional device with high current gain

A resonant-tunneling bipolar transistor (RBT) has been proposed and demonstrated. This is a AlGaAs/GaAs hetero-junction bipolar transistor using a AlAs/GaAs/ AlAs quantum well resonator as a minority carrier injector. The RBT exhibits a collector-current peak with respect to the base-emitter voltage, and therefore a negative transconductance, due to resonant-tunneling of electrons. The common-emitter current gain reaches 20 at 77 K. We also observed a base-current peak due to resonant-tunneling of holes.

Effects of the growth conditions on the incorporation of deep levels in vapor‐grown GaAs

The effects of various conditions on the incorporation of deep levels in VPE GaAs were studied by capacitance spectroscopy. Three kinds of electron traps (Ec−0.86 eV, Ec−0.84 eV, and Ec−0.77 eV) and two kinds of hole traps (EV+0.60 eV and EV+0.44 eV) were measured. Trap concentrations increased strongly with increasing growth rate, but were found to be independent of n‐doping level, type of dopants used (S, Se, Si, Ge, Sn), and growth atmosphere (H2 or N2). These experimental results indicate that the centers responsible for these levels are not due to simple substitutional chemical impurities, but are related to native defects or to complexes involving native defects.

A WSi/TiN/Au Gate Self-Aligned GaAs MESFET with Selectively Grown n+-Layer using MOCVD

A WSi/TiN/Au gate self-aligned GaAs MESFET was formed using MOCVD. The WSi/TiN/Au gate acts as a selective growth mask for the n+-layer. This new process is demonstrated to be effective for reducing the gate resistance and source resistance of FETs simultaneously. The gate resistance, Rg, was 3.4 Ω (Lg=1.3 um, Wg=30 um) and was reduced one tenth compared to that of the WSi gate. A high-speed MSI and high performance microwave device can be obtained by using the WSi/TiN/Au gate self-aligned GaAs MESFETs.

A resonant-tunneling bipolar transistor (RBT): A proposal and demonstration for new functional devices with high current gains

A resonant-tunneling bipolar transistor (RBT) using MBE GaAs/AlGaAs heterostructures has been proposed and fabricated. This device is a bipolar transistor using a quantum well resonator as a hot electron injector. The RBT exhibits a peaked collector-current characteristic with respect to the base-emitter voltage, due to the resonant-tunneling of electrons. The common-emitter current gain reaches 20 at 77K. The device also exhibits a peaked base-current characteristic due to the resonant-tunneling of holes. The measured resonant-tunneling voltages agree well with the simulation results.