J. S. Smith

A new infrared detector using electron emission from multiple quantum wells

A new type of infrared photodetector using free electron absorption in a heavily doped GaAs/GaAlAs quantum well structure has been demonstrated. Preliminary results indicate a strong response in the near infrared with a responsivity conservatively estimated at 200 A/W. The structure can potentially be tailored during fabrication for use in several infrared bands of interest, including the 3 to 5 micron band and the 8 to 10 micron band.

High quality molecular beam epitaxial growth on patterned GaAs substrates

In this letter we describe a procedure for high quality molecular beam epitaxy (MBE) growth over finely patterned GaAs substrates which is suitable for device fabrication requiring lateral definition of small (∼1–2 μm) dimension. This method was used for the fabrication of index guided laser arrays. Yields of individual lasers exceeded 90%, and thresholds were uniform to 10%. Temperature and flux ratio dependence of faceting during MBE growth over patterned substrates is shown for temperatures ranging from 580 to 700 °C and for As/Ga flux ratios from 1.4:1 to 4:1. The real index guided structure, which can be formed by a single MBE growth over a ridged substrate, is discussed. This technique should prove useful in the fabrication of devices which take advantage of unique features formed during regrowth by MBE.

Passive mode locking of buried heterostructure lasers with nonuniform current injection

In this letter we report on a novel method to passively mode lock a semiconductor laser. We present experimental results of GaAlAs buried heterostructure semiconductor laser with a split contact coupled to an external cavity. The split contact structure is used to introduce a controllable amount of saturable absorption which is necessary to initiate passive mode locking. Unlike previous passive mode locking techniques, the method presented does not rely on absorption introduced by damaging the crystal and is consequently inherently more reliable. We have obtained pulses with a full width at half-maximum of 35 ps at repetition frequencies between 500 MHz and 1.5 GHz.

Application of internal photoemission from quantum-well and heterojunction superlattices to infrared photodetectors

Abstract Calculation has been performed for the free carrier and intervalence band absorption in quantum-well structures. Potential application of the enhanced absorptions to near-infrared photodetectors is discussed.

Inverted‐V chirped phased arrays of gain‐guided GaAs/GaAlAs diode lasers

Inverted‐V chirped arrays of multiple quantum well GaAs/GaAlAs lasers were grown by molecular beam epitaxy. These arrays consisted of seven gain‐guided lasers whose stripe widths decreased, from the central laser to the outermost ones, symmetrically. This structure makes it possible to discriminate against the higher order array supermodes, which results in diffraction limited beams with a single lobe directed perpendicular to the laser facet. Single lobed far‐field patterns, 3°–4° wide, were obtained from inverted‐V chirped arrays operated up to 1.5Ith. The supermode structure of these arrays was identified by studying their spectrally resolved near fields.

Streak‐camera observation of 200‐ps recovery of an optical gate in a windowless GaAs étalon array

Fast recovery (<200 ps) of an optical gate at room temperature in a GaAs etalon is observed by eliminating the top AlGaAs window and defining 9×9 μm2 pixels. This recovery time is at least an order of magnitude shorter than that for previous etalons consisting of AlGaAs/GaAs/AlGaAs heterostructures. The fast recovery is attributed to faster surface recombination of carriers at the GaAs‐dielectric mirror interface as compared to that at a GaAs‐AlGaAs interface.

Internal photoemission from quantum well heterojunction superlattices by phononless free-carrier absorption

The possibility of phononless free-carrier absorption in quantum well heterojunction superlattices was investigated. Order of magnitude calculation showed that the absorption coefficient was significantly enhanced over the phonon-assisted process. Important aspects of the enhancement in the design of infrared photodetectors are discussed.

Transmission electron microscopy and photoluminescence study of silicon and boron ion implanted GaAs/GaAlAs quantum wells

Transmission electron microscopy (TEM) and photoluminescence (PL) data are presented on GaAs/Ga0.25Al0.75As quantum well (QW) structures grown by molecular beam epitaxy which were implanted with B ions and Si ions, respectively, to a dose of 1015 cm−2. TEM observations reveal that significant intermixing of the layers occurs in Si implanted QW structures at a depth well beyond the projected range of the implanted ion after 1 h thermal annealing at 850 °C. A subsequent 2‐h annealing causes mixing near the surface, while the unmixed region still remains at a distance twice the projection range. In contrast, intermixing was not observed in annealed B implanted QW structures, which suggests a strong dependence of alloy mixing effects on the impurity. PL data support these results.

Vertical FET's in GaAs

Vertical FETs in GaAlAs material systems have been fabricated. The present structure makes possible extremely short (less than 1000-Å) channel devices which are beyond the reach of optical lithographic processes. Devices with transconductance gmas high as 280 mS/mm have been obtained.

Fabrication and Characterization of Arrays of GaAs All-Optical Logic Gates

Optical bistable elements fabricated from gallium arsenide (GaAs) have demonstrated potential as optical logic elements for use in optical parallel processing systems [1]. In previous experiments, the devices have consisted of small, uniform slabs of active material, either bulk GaAs or GaAs-AlGaAs multiple-quantum-well structures [2]. These were placed between mirrors to form nonlinear Fabry-Perot etalons. The active regions of these earlier devices were grown with top and bottom “windows” of AlGaAs to reduce the exciton surface-recombination rate. The overall switching time of these devices was limited by the carrier relaxation time to several nanoseconds. The present devices were produced from a 1.5-μm-thick GaAs layer, grown by molecular beam epitaxy (MBE) on a single-crystal GaAs substrate with an underlying 0.2-μm-thick Al0.4Ga0.6As etch stop layer, but no top window. The absence of the window resulted in an order-of-magnitude reduction in the recovery time [3]. Some of the wafer was etched to form arrays of small GaAs mesas or “pixels” on a single substrate. The etched surface structure served to further reduce the recovery time, as well as producing an array of separated devices on a single substrate [4]. Each individual pixel of the array measured 9 μm × 9 μm, and the pixels were spaced 20 μm apart from each other (Fig. 1). Individual samples of the array, as mounted in etalons, typically contained several thousands of pixels. However, the fabrication process used for these devices can be easily scaled to larger sizes. Large arrays of optically bistable elements may become important components of powerful optical parallel processing systems. Such processors could make efficient use of the inherent parallelism of optics.