M. McColl

Diffusion Lengths of Electrons and Holes in GaAs

The short‐circuit current of both diffused and n‐type metal semiconductor junctions during 2‐MeV electron irradiation was measured. The results indicate that electron diffusion length in the Zn‐diffused p‐type region is proportional to the reciprocal of the square root of the donor concentration. The electron‐diffusion length ranges from 20 μ for lightly doped diodes to 2 μ for heavily doped diodes. The hole‐diffusion lengths are less than 1.0 μ in heavily doped surface barrier diodes. The thickness of the active radiative recombination region for diffused diodes under forward bias was measured and compared with the short‐circuit current results. These results suggest that the pre‐irradiation electron lifetime is ≈ (10−9 ND)−1, where ND is the substrate donor concentration. This behavior is consistent with radiative recombination between donors and free holes.

The superconductor‐semiconductor Schottky barrier diode detector

The superconductor‐semiconductor contact diode, or super‐Schottky‐barrier‐diode, has been examined theoretically and experimentally as a video detector of high‐frequency radiation. The measured noise‐equivalent power (NEP) of the device is believed to be the smallest value ever reported in the literature for video detection. Moreover, the high reliability established for the ordinary Schottky barrier diode is in evidence for the proposed diode. The doping of the semiconductor is chosen large enough so that electron tunneling dominates the volt‐ampere behavior of the diode. As such, for T < Tc and V < Δ, the diode exhibits a high degree of nonlinearity in its volt‐ampere characteristic. It is this nonlinearity that the super‐Schottky‐diode exploits. Initial results with p‐type GaAs at 1 °K have yielded an NEP of 2 × 10−15 W/Hz1/2 at 10 GHz.

The Super-Schottky Diode

The super-Schottky-barrier diode, a superconductor-semiconductor tunneling junction, has been established as the most sensitive detector of microwaves. These record sensitivities were obtained in both the video and mixing modes of operation. Measurements at X-band have yielded a video NEP of 5 x 10/sup -16/ W/Hz/sup 1/2/ and a mixer input noise temperature of 6 K. The super-Schottky mixer provides a front-end component for ultralow-noise receivers that is superior in bandwidth to available parametric and maser amplifiers and yet has a comparable noise temperature. This article reports the design, fabrication, and measurement of Pb on p-GaAs super-Schottky diodes which perform as nearly ideal low-noise mixers at 9 GHz.

Extension of the Schottky barrier detector to 70 μm (4.3 THz) using submicron‐dimensional contacts

Schottky barrier diode detection in both video and mixing modes of operation has been extended to 4.252 THz (70.5 μm) using 0.5‐μm‐diam diodes fabricated from heavily doped nonepitaxial n‐type GaAs. These ultrasmall, and consequently ultralow capacitance, junctions were prepared using electron‐beam lithography and have yielded the smallest reported series‐resistance junction‐capacitance product for a Schottky barrier diode. The potential for extending diode operation to still higher frequencies is discussed.

Advantages of Mott barrier mixer diodes

It is shown that the high-frequency performance of miter diodes can be appreciably improved by employing a Mort barrier instead of a Schottky barrier. The larger junction diameters possible with Mott structures also allow a better burnout capability and improved mechanical stability.

The super‐Schottky diode microwave mixer

Superconductor‐semiconductor (super‐Schottky) diodes fabricated from Pb on p‐GaAs have been extensively studied as microwave mixers. The measured performance at X‐band is 9‐dB conversion loss and 1.6 K diode noise temperature, resulting in a mixer noise temperature of 13 K. This result is in good agreement with theory and represents a major advance in low‐noise frequency conversion.

Schottky barriers on InSb

Schottky barriers formed on air-cleaved InSb are found to be more reproducible and have less leakage than diodes fabricated by chemical processing. Etched surfaces yield diodes with large leakage currents and high series resistances whose values are correlated, i. e. , high series re-sistances have less leakage and vice versa. With air-cleaved surfaces the lowest leakage is observed when the surfaces adjoining the contact are covered with SiO2. From C-2 versus V data, barrier heights of 50 mV and 175 mV at 77K are measured for Au contacts to n- and p-type InSb, respectively. The current-voltage characteristics of Au contacts are consistent with these barriers, but the low-temperature field-emission behavior appears to be dom-inated by tunneling via traps. For Pb contacts, deep-level traps are in evidence that can lead to erroneous in-terpretations of C-2 versus V voltage intercepts. The I-V data for Pb contacts suggest VBn ≈0 and VBp ≈Eg/q. Diodes fabricated on vacuum-cleaved surfaces have large leakage currents which result from the etching procedures introduced to isolate individual diodes.

Superconductor‐semiconductor device research

Devices and components which combine both superconductors and semiconductors include Josephson and super‐Schottky diodes, superconducting triodes, and hybrids. Semiconductors, such as Si, Ge, Te, GaAs, InAs, InSb, and CdS, are used to form barriers or effective barriers to electron and pair tunneling in the active regions of these devices. Hence such properties as bandgap, barrier height, and mobility become important parameters in tailoring and controlling the device performance. This paper will discuss the motivation for this research, accomplishments to date, and an assessment of the future prospects.

Electrical characterization of metal/inas contacts

Metal contacts to InAs are especially interesting because the surface Fermi level is not stabilized within the forbidden band but is located above the conduction band minimum. The surface of InAs has been investigated by means of electron tunneling experiments which are uniquely sensitive to the surface barrier of p-InAs. The following experimental observations are discussed: the appearance of Esaki-type negative resistance in the forward characteristics of metal/p-InAs contacts; the influence of the metal on this behavior; and the effects of argon ion bombardment and surface preparation on the electrical characteristics. The conclusions are the existence of both a fully inverted surface and an intrinsic interfacial barrier, for both etched and vacuum cleaved surfaces. An estimate of the interfacial barrier properties is presented.

Electron beam fabrication of submicrometer diameter mixer diodes for millimeter and submillimeter wavelengths

Using an electron beam fabrication technique, GaAs Schottky barrier diodes have been produced with submicrometer dimensions, which is a considerable reduction in size over that attainable using conventional photoresist techniques. This advancement should improve the performance of Schottky barrier mixers and detectors at millimeter wavelengths and extend their use to submillimeter wavelengths.