K. Kaviani

Growth of InxGa1−xAs on patterned GaAs(100) substrates

The influence of finite substrate size on misfit dislocation densities in strained systems is examined through the growth of InxGa1−xAs on nonplanar patterned (100) GaAs substrates consisting of parallel mesas of widths between 6500 A and 1.3 μm and of macroscopic length. Cross‐sectional transmission electron microscopy (XTEM) studies on In0.11Ga0.89As films reveal that while the mean misfit dislocation spacing for the growth in the nonpatterned region was ∼1500 A, for the growth on the mesas no misfit dislocations running parallel to the mesa length were observed. This is likely due to strain relief at the mesa edges, possibly brought about by the ability to transfer strain energy from cluster coalescence boundaries to the mesa edges and/or reduced cluster coalescence boundaries when the mesa size becomes comparable to or less than the effective migration length.

Realization and analysis of GaAs/AlAs/In0.1Ga0.9As based resonant tunneling diodes with high peak-to-valley ratios at room temperature

Investigations of pseudomorphic resonant tunneling diodes based on the GaAs/AlAs/In0.1Ga0.9As material system reveal that the use of undoped In0.1Ga0.9As spacer layers gives rise to a significantly enhanced peak‐to‐valley ratio of 3.2 and 14 at 300 and 77 K, respectively, as opposed to 2 and 5 obtained with the use of conventional GaAs spacers in an otherwise identical structure. This is achieved without any significant degradation of the peak current density but rather through reduction of the undesired nonresonant valley current. Comparison of the experimental results with calculations done using the Airy function transfer matrix approach indicates that the Γ‐X discontinuity at the GaAs/AlAs and In0.1Ga0.9 As/AlAs interface is relevant for electron tunneling, along with the smaller transverse effective mass of 0.19m0 in the AlAs X valley. We also find that In0.1Ga0.9As layers grown under an excess As‐stabilized growth condition give better results than those grown under a barely As‐stabilized condition.

Realization of low defect density, ultrathick, strained InGaAs/GaAs multiple quantum well structures via growth on patterned GaAs (100) substrates

Growth of low defect density highly strained InxGa1−xAs/GaAs multiple quantum well (MQW) structures of thicknesses suited for application in spatial light modulator (SLM) devices operating in infrared has been thwarted by the occurrence of strain‐induced defects. Exploiting the notion of strain relief at mesa edges, we report here the first realization of very low defect density MQW structures of thickness as high as 2.38 μm at x=0.20. This has opened up the possibility of realizing a variety of reflective and transmissive SLM structures which also fruitfully exploit the transparent nature of the substrate.

Optimized Oxygen Plasma Etching of Polyurethane‐Based Electro‐optic Polymer for Low Loss Optical Waveguide Fabrication

Oxygen plasma etching of thermosetting polyurethane electro-optic polymers containing disperse red 19 side groups was characterized in detail for making low loss optical waveguides and modulators. The effect of varying parameters such as the RF power, oxygen pressure, and flow rate on optical loss, etching rate, and etching selectivity to photoresist etch mask was studied. These parameters were optimized to minimize the surface roughness in etched areas. By properly choosing the etching conditions, scattering loss due to the surface roughness can be reduced from 0.9 dB/cm to less than 0.1 dB/cm at the wavelength of 1.3 μm, which is much smaller than the absorption loss of the polymer.

High contrast ratio asymmetric Fabry–Perot reflection light modulator based on GaAs/InGaAs multiple quantum wells

We report the realization of both high contrast ratio (66:1) and dynamic range (30%) at room temperature in a strained GaAs/InGaAs(100) multiple quantum well based asymmetric Fabry–Perot reflection modulator. The p‐i‐n configuration modulator also acts as a photodetector and exhibits a high quantum efficiency (∼80%).

Nanofeatures on GaAs (111)B via photolithography

Mesas defined on GaAs(111)B substrates by photolithography followed by wet chemical etching are found to be triangular pyramids with truncated tops. The areal dimensions of the unetched tops of the pyramidal mesas diminish with etch time and can be reduced to an apex on continued etching. Transmission electron microscopy is used to examine a post‐growth etched GaAs/Al0.3Ga0.7As multilayer structure grown on GaAs(111)B. A three‐dimensionally confined GaAs volume of the order of 105 atoms is observed.

Feasibility study of integration of electro-optic polymer waveguide device with MOSFET circuitry on silicon

Systematic development of electro-optic (EO) polymers is leading to optical and material properties such that they present an increasingly viable alternative to crystalline-based technologies for integrated optics. EO polymers demonstrate an inherent velocity match between radio-frequency and optical waves, making them excellent candidates for applications in high-speed telecommunication switching and optical interconnects for VLSI circuitry. In addition, EO polymer devices are relatively simple to fabricate at conditions compatible with microelectronics industry processes, making same-substrate integration of optical and electronic circuitry possible. In this paper, we describe two vertical integration schemes whereby a polymer-based electro-optic modulator may be controlled by metal-oxide semiconductor field effect transistor (MOSFET) circuitry. One scheme described is an insitu integration on the same silicon (Si) substrate. The second scheme is the integration of a modulator built on a flexible substrate with a MOSFET circuit on a second Si substrate. Both schemes have potential applications for integrated electro-optics.

One-step in-situ quantum dots via molecular beam epitaxy

The fabrication and characterization of struc- migration also ensures that the (211) layers are tures with their electronic states confined in three thinner than the (111)B mesa top layers. The dimensions (i.e. quantum dots) is an area of ac- (11 1)B GaAs layers are thus surrounded from all tive research. The maskless one-step in-situ ap- lateral directions by the thinner and thus higher proach that exploits growth kinetics to create band gap GaAs quantum wells growing on the suitable size templates upon which nanostruc- (211) side facets. This difference in band gap tures can be realized via growth alone offers provides the lateral electronic confinement. Verpotential advantages [1] over ex-situ approaches. tical confinement is provided by the AlGaAs layPhotolithography followed by wet chemical ers. The continuous shrinkage of the mesa top etching of the (111)B face of GaAs yields trun- layers results in the mesa pinching off at the 8th

Growth of high quality strained AlxGa1−xAs/In0.26Ga0.74As/AlzGa1−zAs quantum wells and the effect of silicon nitride encapsulation and rapid thermal annealing

We report on the realization of high quality single quantum wells (SQWs) in the highly strained AlxGa1−xAs/In0.26Ga0.74As/AlzGa1−zAs system with 0≤(x, z)≤1.0. Photoluminescence (PL) linewidths of 5.5±0.4 meV for 0.30≤(x and z)≤0.70 have been achieved. Use of both alloys and short period multiple layer structures as the well and/or barrier layers has been examined. The silicon nitride encapsulation as well as rapid thermal annealing (RTA) induced changes in the PL properties of the as‐grown SQW structures have been examined. Deposition of the nitride is found to induce a blue shift in the exciton peak. RTA induces a further blue shift, though not as large as that induced by RTA of unencapsulated (i.e., as‐grown) structures. The RTA induced changes indicate interdiffusion of the group III atoms at the GaAs/InGaAs and InGaAs/AlGaAs interfaces.

Realization of high performance doped-channel MISFETs in highly strained AlGaAs/InGaAs/AlGaAs based quantum wells

Doped channel metal-insulator-semiconductor field effect transistors (DC-MISFETs) in the highly strained AlxGa1-xAs/ In0.26Ga0.74As/AlyGa1-yAs (0<x, y≤1.0) and ((AlAs)m(GaAs)n)/In0.26Ga0.74As/( (AlAs)p (GaAs)q) single quantum wells grown via MBE on GaAs (100) substrates have been examined with a view towards improved performance via control of growth using RHEED behavior of static and dynamic surfaces. Breakdown voltages over 20 V and over 40 V have been realized in structures containing AlGaAs alloy and equivalent Al content short period superlattice (SPSL) barriers, respectively. Low gate leakage currents and output conductance as low as 150 μS/mm have been realized. Increasing the In content to 30% and using heavy Si doping in the well, DC-MISFETs containing SPSL barriers have yielded drain currents of 1.2 A/mm and breakdown voltages of ∼10 V.