J. M. Vandenberg

Strong 8.2 μm infrared intersubband absorption in doped GaAs/AlAs quantum well waveguides

We have measured the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices. Waveguide geometry experiments demonstrate strong absorption with 95% of the incident infrared energy being absorbed.

High‐resolution x‐ray diffraction studies of InGaAs(P)/InP superlattices grown by gas‐source molecular‐beam epitaxy

High‐resolution x‐ray diffraction studies have been carried out to determine the structural perfection and periodicity for a number of high‐quality InGaAs/InP superlattices and one InGaAsP/InP superlattice grown by gas‐source molecular‐beam epitaxy. For comparison, high‐resolution diffraction both with a three‐crystal geometry and with a four‐crystal monochromator was used along with conventional double‐crystal x‐ray diffractometry. The best resolution in the x‐ray satellite patterns was obtained with the four‐crystal monochromator, providing a resolution of one molecular layer in the periodicity of the superlattice. The presence of sharp satellite reflections in the x‐ray diffraction profiles demonstrate smooth interfaces with well‐defined modulated structures which could be derived from a kinematical diffraction step model. For some superlattices, excellent agreement between the step model and the measurements is obtained when the model assumes that each period consists only of the well and the barrier ...

Critical layer thickness in strained Ga1−xInxAs/InP quantum wells

We use a combination of electrical, optical, and structural characterization techniques to determine the critical layer thickness of strained Ga1−xInxAs/InP quantum wells. Well compositions covering the entire range of strain available, from −3.8% (GaAs) to +3.2% (InAs), were investigated. We find that the critical layer thickness in this material system is unambiguously described by the classical Matthews and Blakeslee force balance model [J. Cryst. Growth 27, 118 (1974)]. Reverse leakage current of strained‐well samples grown in a p‐i‐n configuration is shown to be the most direct and reliable measure of the pseudomorphic limit.

Admittance spectroscopy measurement of band offsets in strained layers of InxGa1−xAs grown on InP

We report measurements of the conduction‐band offset in strained‐layer superlattices of InxGa1−xAs/InP. Admittance spectroscopy was used to measure the activation energy for thermionic emission of electrons over InP barriers in n‐type superlattices. Superlattice dimensions and x values were obtained from high‐resolution x‐ray diffraction and transmission electron microscopy studies. For x=0.37, 0.53, and 0.69, the values obtained for the conduction‐band offset are 175±25 meV, 210±20 meV, and 315±25 meV, respectively.

GaInAs(P)/InP quantum well structures grown by gas source molecular beam epitaxy

We describe optical properties of single and multiple quantum well structures grown by gas source molecular beam epitaxy. Absorption and photoluminescence were used in conjunction with x‐ray and transmission electron microscopy techniques to determine the confined particle energy levels and well thicknesses. Well defined exciton transitions were observed in the ternary and quaternary well superlattices even above room temperature. In single well structures energy shifts as large as 260 and 370 meV were observed for GaInAs and GaInAsP wells, respectively. On the basis of these results we estimated that over 50% of the InGaAs/InP band discontinuity resides in the conduction band.

Structural study of alloyed gold metallization contacts on InGaAsP/InP layers

Specific contact resistance of gold metallization on In1−xGaxAsyP1−y has been measured as a function of composition from InP to In0.53Ga0.47As. The alloy formation of the contacts was investigated in the temperature range 130°–550°C, using temperature dependent in situ x‐ray diffraction. The thermodynamics of the solid state reactions are discussed. The electrical contact behavior can be explained in terms of the alloys which form at various temperatures. In the ternary Au/InGaAs/InP contact polycrystalline GaAs and a thin layer of Au3In2 form at lower temperatures (150°–250 °C) and remain stable up to 550 °C. This is consistent with the measured low contact resistance which is comparable to that of the Au/GaAs contact.

Intrinsic strain at lattice-matched Ga0.47In0.53As/InP interfaces as studied with high-resolution x-ray diffraction

High‐resolution x‐ray studies of Ga0.47In0.53As/InP superlattices reveal, for the first time, the presence of an intrinsic interfacial strain at heteroepitaxial interfaces. This strain is produced by an asymmetric ordering of the atomic layers in the leading and trailing interfaces of each quantum well as the result of the normal growth sequence during gas source molecular beam epitaxy.

High‐resolution x‐ray diffraction and transmission electron microscopy studies of InGaAs/InP superlattices grown by gas‐source molecular beam epitaxy

A three‐crystal geometry has been used for high‐resolution x‐ray diffraction (XRD) along with lattice imaging transmission electron microscopy (TEM) to study two high‐quality InGaAs/InP multiquantum well structures grown on (100) InP. These superlattices were prepared by gas‐source molecular beam epitaxy using a computer controlled system and were found to have excellent optical properties. Cross‐section TEM and the presence of sharp satellite reflections in the XRD profiles demonstrate very smooth interfaces with well‐defined modulated structures which could be derived from a kinematic XRD step model. For one of these superlattices, excellent agreement between the step model and the measurements is obtained when the model assumes that each period consists only of the well and the barrier with ideally sharp interfaces. For the other superlattice an additional approximately 9‐A‐thick layer of approximate composition In0.47Ga0.53As0.985P0.015 had to be assumed on one side of each quantum well. This addition...

Structural perfection of InGaAs/InP strained‐layer superlattices grown by gas source molecular‐beam epitaxy: A high‐resolution x‐ray diffraction study

High‐resolution x‐ray diffraction (HRXRD) studies have been carried out to determine the structural perfection and periodicity for a number of high‐quality InGaAs/InP strained‐layer superlattices grown by gas source molecular‐beam epitaxy. X‐ray scans were carried out with a compact four‐crystal monochromator resulting in a resolution of one molecular layer (∼3 A), which enables one to observe very small variations in the periodic structure. Sharp and strong higher‐order satellite reflections in the XRD profiles were observed indicating smooth interfaces with well‐defined modulated structures. Excellent computer simulated fits of the x‐ray satellite pattern could be generated based on a kinematical XRD step model which assumes ideally sharp interfaces. Our results demonstrate that HRXRD in conjunction with the kinematical step model provides a powerful tool to evaluate the structural perfection of InGaAs/InP strained‐layer superlattices.

Strained quaternary quantum well lasers for high temperature operation

We describe compressively strained separate confinement heterostructure 1.3 μm quantum well lasers optimized for high temperature operation. The active layer consists of ten GaInAsP wells, each 40–80 A thick, grown under compressive lattice mismatch strain of Δa/a≤0.75%. Within the constraints of the well composition and thickness imposed on the active region, strain is necessary for efficient laser operation. Best results are obtained for Δa/a∼0.2%–0.3% with the laser threshold as low as 5 mA and slope efficiency of 42 mW/mA. In the temperature range of 25–85 °C a slope efficiency change as small as 30% was achieved. Power output of at least 20 mW can be maintained up to 100 °C at a current drive below 150 mA.