W.C.B. Peatman

GaAs Schottky diodes for THz mixing applications

The operation of GaAs Schottky barrier diodes, the critical mixer element used in heterodyne receivers for a variety of scientific applications in the terahertz frequency range, is reviewed. The constraints that the receiver system places on the diodes are considered, and the fundamental guidelines for device optimization are presented. The status of ongoing research, both experimental and theoretical, is examined. Emphasis is placed on investigations of the various effects that can limit diode performance at these high frequencies. Investigations of planar diode technology are summarized, and the potential replacement of whisker-contacted devices with planar structures is considered. >

A novel Schottky/2-DEG diode for millimeter- and submillimeter-wave multiplier applications

A high-frequency diode is proposed for use as a frequency multiplier element in the millimeter- and submillimeter-wavelength regions. The Schottky/2-DEG diode utilizes a Schottky contact along the edge of a two-dimensional electron gas (2-DEG) structure. This geometry allows one to combine a very low series resistance due to the excellent transport properties of the 2-DEG with a high breakdown voltage caused by the 2-D electric field spreading in the depletion region (compared to a 1-D field variation in the conventional Schottky diode). The higher Fermi velocity of the 2-DEG leads to a less severe transit-time limitation of the frequency response.<<ETX>>

Design and fabrication of 0.5 micron GaAs Schottky barrier diodes for low-noise terahertz receiver applications

Recent technological advances have made possible the development of heterodyne receivers with high sensitivity and high spectral resolution for frequencies in the range 1,000–3,000 GHz (1–3 THz). These receivers rely on GaAs Schottky barrier mixer diodes to translate the high-frequency signal to a lower frequency where amplification and signal processing are possible. At these frequencies, the diode quality is a major limitation to the performance of the receiver. The design, fabrication and DC evaluation of a diode for this frequency range is presented. A figure-of-merit cut-off frequency of over 10 THz is achieved with a record low zero biased capacitance of 0.5 fF. Results from RF tests are also given.

Novel resonant tunneling transistor with high transconductance at room temperature

A resonant tunneling transistor (RTT) utilizing a novel heterodimensional Schottky gate technology is described. The gate is formed by electroplating Pt/Au onto the side of an AlGaAs/GaAs double barrier structure. The gate voltage modulates the drain current by modulating the area of the quasi-two dimensional electron accumulation layer which forms above the source barrier under drain-source bias. Room temperature transistor characteristics included a peak current of 225 mA/mm and peak transconductance of 218 mS/mm. The ultrafine fabrication process is also discussed.<<ETX>>

Enhancement of Schottky barrier height in heterodimensional metal-semiconductor contacts

We report on the measurements of the heterodimensional Schottky barrier height in two-dimensional metal-semiconductor field effect transistors (2D MESFETs). Our experimental data indicate approximately 0.1 eV greater barrier height compared to conventional metal-semiconductor contacts of the same materials. The enhancement is explained in terms of two effects—quantization of energy levels of the carriers in the quantum well and broadening of the corresponding wave functions. The increased barrier height leads to a substantial reduction of the gate leakage current in 2D MESFETs.

Narrow channel 2-D MESFET for low power electronics

A 2-D MESFET utilizing sidewall Schottky contacts on either side of a very narrow 2-d electron gas channel is described. Record transconductance of 295 and 130 mS/mm have been achieved at room temperature in 1.0 and 0.5 micron wide devices, respectively. We also present accurate 2-D MESFET current-voltage and capacitance-voltage models. These models have been implemented into AIM-Spice which was used to simulate DCFL inverter and ring oscillator circuits. The ring oscillator simulations predict a power-delay product of less than 0.1 fJ/gate at room temperature, suggesting that the 2-D MESFET may be useful for ultra low power electronics applications. >

Two-dimensional metal-semiconductor field effect transistor for ultra low power circuit applications

We describe a novel 2-dimensional metal-semiconductor field effect transistor (2-D MESFET) in which opposing Schottky side gates formed on the sidewall of a modulation-doped AlGaAs-InGaAs heterostructure modulate the channel width and the drain current. The drain current ranged from 0 to 210 /spl mu/A and the maximum measured transconductance was 212 /spl mu/S (212 mS/mm) at room temperature for a 1/spl times/1 micron channel. The threshold voltage was -0.45 V and the subthreshold ideality factor was 1.30. The estimated gate capacitance was 0.8 fF//spl mu/m, or about half the equivalent capacitance of conventional HFETs. The cutoff frequency f/sub T/ was estimated to be 21 GHz. The narrow channel effect, which limits the minimum power consumption in conventional FETs, is practically eliminated in this device.<<ETX>>

Investigation of GaAs Schottky barrier diodes in the THz range

The properties of GaAs Schottky barrier diodes as video detectors and mixing elements were investigated in the frequency range from 0.8–2.5 THz. For the most sensitive diode, the video responsivity and system noise temperature were measured as a function of incident laser power. The highest video responsivity was 2,000 V/W at 214μm and 60 V/W at 118μm. For five diodes differing in doping, capacitance, series resistance and anode diameter, the system noise temperature was measured at 214μm and 118μm. The best single sideband (SSB) values are 12,300 K and 24,200 K at 214μm and 118μm, respectively. The system noise temperature versus frequency is given over the range from 0.5–3 THz for two specific diodes demonstrating that the sharpness of the I–V characteristics is only of secondary importance for mixer perfomance at such high frequencies.

Quarter‐micrometer GaAs Schottky barrier diode with high video responsivity at 118 μm

A quarter‐micrometer diameter Schottky barrier mixer diode has been fabricated on n+ GaAs using electron beam lithography and reactive ion etching (RIE). The anodes were formed using a Pt/Au electroplate technique. The diode zero‐bias capacitance of 0.25 fF and series resistance of about 25 Ω, measured at dc, correspond to a ‘‘figure‐of‐merit’’ cuttoff frequency of about 25 THz. The video responsivity at 118 μm (2540 GHz) was as high as 200 V/W, over three times higher than the best previously reported. The design, fabrication, and evaluation of this diode is described.

Novel heterodimensional diodes and transistors

Abstract We describe novel heterodimensional devices which utilize Schottky barriers to a two-dimensional (2D) electron gas. These devices include a 2D–3D Schottky diode, an AlGaAs GaAs Schottky Gated Resonant Tunneling Transistor (SGRTT), an AlGaAs InGaAs 2D Metal Semiconductor Field Effect Transistor (2D MESFET), and a Coaxial MESFET. These devices hold promise of ultra low power, high speed operation. The 1 micron wide 2D MESFET, which has a very low output conductance and a steep subthreshold slope, exhibited the highest transconductance of any 1 μm wide device.