Michael B. Santos

Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording

A mesoscopic nonmagnetic magnetoresistive read-head sensor based on the recently reported extraordinary magnetoresistance (EMR) effect has been fabricated from a narrow-gap Si-doped InSb quantum well. The sensor has a conservatively estimated areal-density of 116 Gb/in.2 with a 300 K EMR of 6% and a current sensitivity of 147 Ω/T at a relevant field of 0.05 T and a bias of 0.27 T. Because this sensor is not subject to magnetic noise, which limits conventional sensors to areal densities of order 100 Gb/in.2, it opens a pathway to ultra-high-density recording at areal densities of order 1 Tb/in.2.

High-indium-content InGaAs metal-oxide-semiconductor capacitor with amorphous LaAlO3 gate dielectric

The structure and electrical properties of LaAlO3∕n-In0.53Ga0.47As metal-oxide-semiconductor capacitors deposited by molecular-beam epitaxy were investigated. Transmission electron microscopy revealed a sharp interface between the dielectric and InGaAs. Postdeposition annealing at 440–500°C significantly reduced the capacitive equivalent thickness and frequency dispersion. A hysteresis of 15mV–0.1V, a dielectric permittivity of 17±1, and a dielectric strength of ∼4.3MV∕cm were measured. Additionally, a high loss in the parallel conductance and gate-bias independence in the inversion region was observed, implying the fast generation rate of minority carriers in In0.53Ga0.47As.

Interband cascade photovoltaic devices

A photovoltaic (PV) device based on an interband cascade (IC) structure is proposed for efficiently converting solar and thermal energy to electricity. These IC PV devices employ absorption and transport regions with characteristics that are favorable for achieving high open-circuit voltage and thus possibly improving conversion efficiency over conventional PV devices. Preliminary experiments carried out using IC infrared photodetectors (seven stages) and lasers (11 stages) showed open-circuit voltages that exceed the single-band gap voltage from these devices under infrared illumination. The observed open-circuit voltage demonstrates multiple stages operating in series and provides an initial proof of concept for IC PV devices.

Room temperature extraordinary magnetoresistance of nonmagnetic narrow-gap semiconductor/metal composites: application to read-head sensors for ultrahigh-density magnetic recording

The room temperature extraordinary magnetoresistance (EMR) of a mesoscopic sensor structure prepared from an InSb quantum well of dimension 30 nm wide/spl times/100 nm high/spl times/3 /spl mu/m long is reported. The observed EMR is 4.75% at a relevant field of 0.05 T. The advantages and disadvantages of this nonmagnetic composite semiconductor/metal structure relative to that of conventional magnetic giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices for use as read-heads in high-density magnetic recording are discussed.

Determination of the concentration and temperature dependence of the fundamental energy gap in AlxIn1−xSb

We use transmission spectroscopy to determine the energy gap for the AlxIn1−xSb alloy system in the Al concentration range from 0% to 25% from cryogenic to room temperature. The samples are epitaxial layers grown by molecular beam epitaxy on GaAs substrates. Our room temperature results are compared to those from two earlier studies. In our Al concentration range, we find a linear change of energy gap with alloy lattice constant.

Molecular beam epitaxy of InSb on Si substrates using fluoride buffer layers

The molecular beam epitaxy of InSb/Si structures was accomplished using group IIa fluoride buffer layers. InSb growth was initiated by opening the In and Sb shutters simultaneously at substrate temperatures between 300 °C and 400 °C, producing In-terminated InSb(111)-A surfaces on CaF2/Si(111) substrates. Reflection high-energy electron diffraction, electron channeling, and high resolution x-ray diffraction measurements indicated that the InSb layers were of good crystalline quality. Electron mobilities at room temperature were as high as 65 000 cm2/V s for an 8-μm-thick InSb layer grown on CaF2/Si(111). On CaF2/Si(001) substrates, the InSb layers grew in the (111) orientation with two domains 90° apart. These InSb layers and ones grown on BaF2/CaF2/Si(111) substrates exhibited inferior electrical and structural properties compared to structures grown on CaF2/Si(111) substrates.

Spin-polarized reflection in a two-dimensional electron system

We present a method to create spin-polarized beams of ballistic electrons in a two-dimensional electron system in the presence of spin–orbit interaction. Scattering of a spin-unpolarized injected beam from a lithographic barrier leads to the creation of two fully spin-polarized side beams, in addition to an unpolarized specularly reflected beam. Experimental magnetotransport data on InSb∕InAlSb heterostructures demonstrate the spin-polarized reflection in a mesoscopic geometry.

Plasmon-Waveguide Interband Cascade Lasers Near 7.5

Broad-area plasmon-waveguide interband cascade lasers with emission wavelengths near 7.5 mu m were demonstrated at temperatures up to 121 K in continuous-wave mode. Their threshold current densities and voltages varied from 72 A/cm2 and 2.1 V at 84 K to 400 A/cm2 and 2.7 V at 121 K, showing very efficient use of bias voltage (e.g., voltage efficiency of about 90% at 84 K) at this long wavelength. These plasmon-waveguide lasers also operated in pulsed mode at temperatures up to 165 K with emission wavelengths near 7.6 mum and threshold current density of 1100 A/cm2.

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Electrically tunable interband cascade lasers are demonstrated with a wide tuning range of about 280 cm−1 (34 meV in energy or 630 nm in wavelength) near 4.5 μm and about 180 cm−1 (22 meV or 900 nm) near 7 μm wavelengths. The laser structures are designed such that the heating and Stark effects act together to enhance the red-shift of the lasing wavelength with current injection to achieve wide tunability. The control and manipulation of the tuning range and rate are discussed.

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InAs-based interband cascade (IC) lasers with improved optical confinement have achieved high-temperature operation with a threshold current density as low as 247 A/cm2 at 300 K for emission near 4.6 μm. The threshold current density is the lowest ever reported among semiconductor mid-infrared lasers at similar wavelengths. These InAs-based IC devices lased in pulsed mode at temperatures up to 377 K near 5.1 μm. Narrow-ridge devices were able to operate in continuous-wave mode at temperatures up to 308 K near 4.8 μm. The implications and prospects of these results are discussed.