Experiments on ultra‐small metal‐oxide‐semiconductor field effect transistors (MOSFETs) less than 100 nm have been widely reported recently. The frequency of carrier scattering events in these ultra‐small devices is diminished, so that further suppression of carrier scattering may bring these devices close to the regime of ballistic transport. Carrier scattering is suppressed by constructing their channel regions with intrinsic Si and also by low temperature operation. This article proposes the ballistic transport of carriers in MOSFETs, and presents the current‐voltage characteristics of the ballistic n‐channel MOSFET. The current is expressed with the elementary parameters without depending on the carrier mobility. It is independent of the channel length and is proportional to the channel width. The current value saturates as the drain voltage is increased and the triode and the pentode operation are specified as in the conventional MOSFET. Similar current‐voltage characteristics in the ballistic transport regime are also investigated for the p‐channel MOSFET, the dual gate ultra‐thin silicon on insulator MOSFET, and the high electron mobility transistor device. The obtained current gives the maximum current limitation of each field effect transistor geometry. The current control mechanism of ballistic MOSFETs is discussed. The current value is governed by the product of the carrier density near the source edge in the channel, and the velocity with which carriers are injected from the source into the channel.Influence of optical phonon emission to the transport is discussed. It is suggested that if the device is operated with relatively low carrier density at low temperatures, and if the scattering processes other than the optical phonon emission are suppressed so as to attain the ballistic transport, the optical phonon emission is also suppressed and ballistic transport is sustained. A convenient figure of merit to show the ballisticity of carrier transport in an experimental MOSFET is proposed. Its value is estimated for some examples of the recent ultra‐small MOSFET experiment. The proposed current voltage characteristics are evaluated for a dual gate silicon on insulator MOSFET geometry. The result is compared with the recently reported elaborate Monte Carlo simulation with satisfactory agreement.

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Ballistic metal-oxide-semiconductor field effect transistor

The buffer is grown by molecular beam epitaxy (MBE) at low substrate temperatures (150-300 degrees C) using Ga and As/sub 4/ beam fluxes. It is highly resistive, optically inactive, and crystalline, and high-quality GaAs active layers can be grown on top of the buffer. MESFETs fabricated in active layers grown on top of this new buffer show improved output resistance and breakdown voltages; the DC and RF characteristics are otherwise comparable to MESFETs fabricated by alternative means and with other buffer layers. >

New MBE buffer used to eliminate backgating in GaAs MESFETs

Theoretical calculations have been developed for a two-dimensional electron gas FET (TEGFET) constituted by a AlGaAs (n)-GaAs (n-or p-) heterostructure in which the Schottky gate is deposited on the AlGaAs(n) top layer. The theory takes into account: i) the subband splitting in the two-dimensional electron gas (2-DEG); and ii) the existence of an undoped AlGaAs spacer layer which has been found to enhance the electron mobility. The sheet carrier concentration of the TEGFET has been calculated, and a simple analytical formula has been established for the charge control in large and small gate FET.

Metal-(n) AlGaAs-GaAs two-dimensional electron gas FET

For more than three decades, SiC has been investigated as a wide band gap semiconductor. This paper reviews ohmic and rectifying metal contacts on n- and p-type α- and β-SiC reported throughout that time period. Electrical characteristics, Schottky barrier heights (SBHs), thermal stability, and chemical reactions are discussed. Most metals formed very good rectifying contacts in the as-deposited condition on both n- and p-type 6H-SiC with Schottky barrier heights ⪖ 1 eV. Low ideality factors (n 1100 V) have been displayed in this material. The electrical properties of contacts on 3C-SiC have been more dependent on the quality of the 3C-SiC films, which have been plagued by higher defect densities than 6H-SiC. In general, a partial pinning of the Fermi level has been evidenced by positive correlations, which are less than 1 (≈ 0.2–0.6), between the SBHs and the metal work functions. Ohmic contacts with low contact resistivities (⪕ 10−5 Ω cm2), especially important for high power applications, on any of the SiC polytypes have been exceptionally difficult to achieve. Most of the ohmic contacts have relied on high doping concentrations in combination with annealing at temperatures between 800 and 1300 °C. Annealed Ni and Al have primarily been used in ohmic contact metallizations for n- and p-type SiC, respectively. The tendency of SiC to react with metals to form carbides and/or silicides at potential device operating temperatures ( ∼ 600 °C) can be a problem for potential long term applications at high temperature. These critical issues are discussed along with future perspectives for research approaches.

A critical review of ohmic and rectifying contacts for silicon carbide

An overview of ohmic contacts on solar cells is presented The fundamentals of metal-semiconductor contacts are reviewed, including the Schottky approach, Fermi level pinning by surface states, and the mechanisms of thermionic emission, thermionic/field emission, and tunneling for current transport The concept of contact resistance is developed and contact resistance data for several different contact materials on both silicon and gallium arsenide over a range of doping densities are summarized Finally, the requirements imposed by solar cells on contact resistance are detailed

Solar cell contact resistance&#8212;A review

A new majority carrier rectifying device is demonstrated which is made in gallium arsenide by molecular beam epitaxy. It exhibits thermionic transport with positive and negative bias and the barrier height and degree of asymmetry in the I/V characteristic can be continuously varied. The device also shows a constant capacitance with bias.

Planar-doped barriers in GaAs by molecular beam epitaxy

Nonalloyed ohmic contacts to n-GaAs with contact resistances (ρc) below 1·0×10−7 Ω cm2 have been obtained using a Ge/GaAs heterojunction system. Metals are evaporated on heavily arsenic-doped germanium (Ge) layers grown on GaAs. Low values of ρc result from the low Schottky barrier height (≈ 0·50 eV) and the high doping levels obtainable for n-Ge(≈ 1020 cm−3).

Ultra low resistance ohmic contacts to n-GaAs

Deep levels in GaAs grown by molecular-beam epitaxy have been examined. Dependence of both electron and hole trap densities on growth parameters such as growth temperature have been obtained.

Growth-parameter dependence of deep levels in molecular-beam-epitaxial GaAs

Experimental current/voltage characteristics are described for n+-n-n+ and n+-p−-n+ GaAs structures. It is evident from the results that the electron transport is mainly ballistic in nature.

Ballistic electron motion in GaAs at room temperature

Molecular beam epitaxy has been used in a continuous growth procedure to form GeGaAs epitaxial structures that were suitable for MESFET fabrication. Near surface doping profiles were engineered such that low resistance ohmic contacts to the GaAs layer were obtained by subsequently depositing a metal overlayer on the Ge surface. Evaporated Au overlayers yielded specific contact resistances of the order of 10−6ω cm2 without heat treatment. Because the conventional alloying procedure now appeared superfluous, metallurgically non-reactive systems were investigated with a view to constructing GaAs MESFETs with entirely refractory metallizations. Sputtered molybdenum has been evaluated for both the formation of ohmic contacts to the Ge/GaAs layers and rectifying contacts to the GaAs layer. Damage introduced as a result of the sputtering deposition process is the probable cause of non-ideality in the as-prepared Schottky barriers. However, forward bias current-voltage ideality factors of n = 1.07 have been obtained after annealing.

C.E.C. Wood

Papers

Planar-doped barriers in GaAs by molecular beam epitaxy

Ultra low resistance ohmic contacts to n-GaAs

Growth-parameter dependence of deep levels in molecular-beam-epitaxial GaAs

Ballistic electron motion in GaAs at room temperature

A molybdenium source, gate and drain metallization system for GaAs MESFET layers grown by molecular beam epitaxy