Dale L. Partin

Narrow-gap semiconductor magnetic-field sensors and applications

Narrow-gap semiconductors have been used for decades in the fabrication of magnetic field sensors, such as magnetoresistors and Hall sensors. Magnetic field sensors are, in turn, used in conjunction with permanent magnets to make contactless potentiometers and rotary encoders. This sensing technology offers the most reliable way to convert a mechanical movement into an electrical signal, and is widespread in automotive applications. Recent developments in the growth of thin epitaxial layers of InAs and InSb on semiinsulating GaAs or InP substrates have resulted in the development of magnetoresistors with excellent sensitivity and operating temperatures up to 285 degrees C. Magnetoresistors and Hall sensors require a very thin active semiconductor region, a high carrier density and a high room-temperature mobility. The best materials are narrow-gap III-V compounds. 2DEG layers in InSb and InAs would be ideally suited for these devices. The accumulation layer at the surface of InAs has been used to make magnetoresistors, Hall sensors and magnetotransistors. n-type doped thin InSb films are used to make magnetoresistors that outperform Si-based Hall sensors, even with integrated amplification. The authors describe device design criteria, materials requirements and a direct comparison of the three types of galvanomagnetic devices, magnetoresistors, Hall sensors and magnetotransistors, made from the same material. They compare the output of different magnetic field sensing technologies, such as Si and GaAs Hall sensors, and NiFe-based magnetoresistors, with InSb magnetoresistors.

Lead salt quantum well diode lasers

Abstract Lead-salt diode lasers are useful for spectroscopic applications in the 2.5–30 μm wavelength range. These devices have previously required cryogenic cooling

Lead-europium-selenide-telluride grown by molecular beam epitaxy

The band gap of lead-europium-telluride (Pb1-x EuxTe) was determined from room temperature optical absorption measurements and increases as dEg/dx = 3.5 eV for x ≤ 0.044. Eu atoms bond strongly to a PbTe surface during MBE growth and have a small diffusion coefficient (<1 x 10−16 cm /sec at 370°C). The lattice constant of Pb1-x, Eux Te is a nonlinear function of composition, and lattice-matched growth of Pb1-x Eux Sey Te1-y, on PbTe is demonstrated. Preliminary studies of the electrical properties of Pb1-x Eux Te indicate compensation of n-type (Bi) and p-type (Tl) dopants. These results indicate that Pb1-x Eux Sey Te1-y, may be useful for obtaining diode lasers which emit at wavelengths shorter than those available from Pb1-x, Snx Te.

Integrated magnetic field sensor

A magnetic field sensor, such as a magnetoresistor, includes a strip of a layer of a high electron mobility semiconductor whose electrical characteristics vary when a magnetic field is applied thereto on the surface of a body (substrate) of an insulating layer. Conductive contacts are on the strip at the ends thereof and conductive shorting bars are on and spaced along the strip to divide the strip into active regions. The body is mounted on a permanent magnet assembly which includes a magnet and a layer of a ferromagnetic material with the ferromagnetic material extending over the strip. The ferromagnetic layer is in close proximity to only the strip and, more preferably, to only the active regions of the strip so as to confine the magnetic field to the strip.

Evolution of structural and electronic properties of highly mismatched InSb films

We have investigated the evolution of structural and electronic properties of highly mismatched InSb films, with thicknesses ranging from 0.1 to 1.5 μm. Atomic force microscopy, cross-sectional transmission electron microscopy, and high-resolution x-ray diffraction show that the 0.1 μm films are nearly fully relaxed and consist of partially coalesced islands, which apparently contain threading dislocations at their boundaries. As the film thickness increases beyond 0.2 μm, the island coalescence is complete and the residual strain is reduced. Although the epilayers have relaxed equally in the 〈110〉 in-plane directions, the epilayer rotation about an in-plane axis (epilayer tilt) is not equal in both 〈110〉 in-plane directions. Interestingly, the island-like surface features tend to be preferentially elongated along the axis of epilayer tilt. Furthermore, epilayer tilt which increases the substrate offcut (reverse tilt) is evident in the [110] direction. High-resolution transmission electron microscopy indi...

Single quantum well lead‐europium‐selenide‐telluride diode lasers

It is desirable to increase the operating temperature of long wavelength lead‐chalcogenide diode lasers to simplify cooling system requirements. Recently, double heterostructure Pb1−xEuxSeyTe1−y diode lasers (grown by molecular beam epitaxy) operated up to 147 K cw (180 K pulsed). The output photon energy of these devices is linear with x in the wavelength range 6.6– 2.7 μm. The growth of single quantum well lead‐chalcogenide diode lasers is now reported for the first time. These devices had PbTe quantum wells with PbEuSeTe confinement layers. The width of the quantum wells, Lz, was varied from 300 to 250 A. Strong quantum effects are observed for Lz ≲ 1200 A because of the small carrier masses (me∼mh∼0.04mo ). The shift in laser emission energy is in approximate agreement with that calculated from a finite square well potential. At low temperatures (≲100 K), these lasers appear to operate on transitions between n=1 states in the conduction and valence bands at threshold. Transitions between the n=2 state...

Wavelength coverage of lead‐europium‐selenide‐telluride diode lasers

Diode lasers made from a new semiconductor material, Pb1−xEuxSeyTe1−y, have recently been developed for sensor applications. This material is grown by molecular beam epitaxy and may be lattice matched to PbTe substrates. Double heterojunction mesa stripe diode lasers have been fabricated and the laser emission energy determined as a function of composition. At 80 K, the emission energy follows the relation E (in eV)=0.219+5.51x. With the range of active region compositions so far explored (up to x=0.046, y=0.054), the wavelength range 6.6–2.6 μm can be covered under pulsed conditions (6.6–3.8 μm cw). Laser operation up to 190 K pulsed, 147 K cw, has been attained with up to 1‐mW single mode output power. These devices are useful for spectroscopic measurements of molecules in a gas or adsorbed onto surfaces.

Effects of buffer layers on the structural and electronic properties of InSb films

We have investigated the effects of various buffer layers on the structural and electronic properties of n-doped InSb films. We find a significant decrease in room-temperature electron mobility of InSb films grown on low-misfit GaSb buffers, and a significant increase in room-temperature electron mobility of InSb films grown on high-misfit InAlSb or step-graded GaSb+InAlSb buffers, in comparison with those grown directly on GaAs. Plan-view transmission electron microscopy (TEM) indicates a significant increase in threading dislocation density for InSb films grown on the low-misfit buffers, and a significant decrease in threading dislocation density for InSb films grown on high-misfit or step-graded buffers, in comparison with those grown directly on GaAs. Cross-sectional TEM reveals the role of the film/buffer interfaces in the nucleation (filtering) of threading dislocations for the low-misfit (high-misfit and step-graded) buffers. A quantitative analysis of electron mobility and carrier-concentration de...

Temperature stable Hall effect sensors

Magnetic field sensors are needed for high-accuracy position, angle, force, strain, torque, and current flow measurements. Molecular beam epitaxy was used to grow tellurium-doped indium-gallium antimonide thin films. Hall effect sensors made from these films have been studied for their magnetic sensitivity and thermal stability. For a range of alloy composition near In/sub 0.8/Ga/sub 0.2/Sb and n-type doping levels near 2/spl times/10/sup 17/ cm/sup -3/, high magnetic sensitivity from -40/spl deg/C to +200/spl deg/C was found with a resolution of better than /spl plusmn/0.5% over the entire temperature range.

Growth of high mobility InSb by metalorganic chemical vapor deposition

Thin films of InSb have been grown on insulating GaAs substrates using the metalorganic chemical vapor deposition technique with trimethyl indium and trimethyl antimony as reactants. We find that the mobilities obtained are usually low unless indium is predeposited onto the substrate. This indium predeposition technique greatly improves the yield of InSb films with mobilities of ~50000 crn2V−1S−1 at room temperature and a typical thickness of 2 microns. With this predeposition technique, the electron mobilities of these films become relatively independent of the vapor stroichiometry during growth and of the growth temperature. The electron mobilities are also very uniform across a wafer. These properties are obtained even when the film growth rate exceeds 2 μm/h.