Superlattice Buffer Layer Research Articles

Low-loss AlGaAs optical rectangular waveguides at 830 nm

Optical channel waveguides with rectangular cross section and losses less than 0.1 dB/cm at 830 nm have been fabricated in AlGaAs heterostructures grown by organometallic vapor phase epitaxy. The modal attenuation correlates with surface morphology for all waveguide widths and with sidewall roughness for narrow channels. Surface morphology and modal attenuation improve when a superlattice buffer layer is incorporated into the structure. The loss is also reduced when the arsenic source (arsine) is purified in-line.

Quantum-confined field-effect light emitters: device physics and experiments

Extended experimental results on three-terminal quantum-confined field-effect light emitters with current injection and field control of luminescent characteristics in the quantum-well structure are reported. By incorporating superlattice buffer layers (SLBLs), the quantum efficiency of the device is dramatically improved and equivalently nonradiative recombination processes are sufficiently suppressed at room temperature. The red-shift of the emission spectra by the quantum-confined Stark effect assures that the electric field is effectively applied to the quantum well. The experimental data on the transient responses of emission intensity to input voltage pulses show fairly good correspondences with theoretical prediction and previous photoluminescence experiments. The authors discuss the ultimate capability of high-speed switching and point that an optical pulse with a duration as short as 30 ps and involving more than 100 photons can be generated by scaling down the size of the device with 1% external efficiency. >

Growth of single-crystal metastable (GaAs)1−x(Si2)x alloys on GaAs and (GaAs)1−x(Si2)x/GaAs strained-layer superlattices

Epitaxial zinc blende structure metastable (GaAs)1−x(Si2)x alloys have been grown with 0<x<0.3 on As-stabilized GaAs(100) substrates by a hybrid sputter deposition/evaporation technique. The films, typically 2–3 μm thick, were deposited at 570 °C with growth rates between 0.7 and 1 μm h−1. Alloys with 0<x<0.12 were defect-free as judged by plan-view and cross-sectional transmission electron microscopy (TEM and XTEM) with x-ray diffraction peak widths approximately the same as that of the substrate, 30 arcsec 2θ. XTEM lattice images showed smooth abrupt interfaces. (GaAs)1−x(Si2)x alloys with x>0.12 exhibited increasing evidence of interfacial defects associated with lattice strain when grown on GaAs. However, defect-free alloys with x up to 0.3 were obtained using (GaAs)1−x(Si2)x/GaAs strained-layer superlattice buffer layers to provide a better lattice match.

Reduction in interfacial recombination velocity by superlattice buffer layers in GaAs/AlGaAs quantum well structures

The values of interfacial recombination velocities in GaAs/AlGaAs double heterostructures and quantum wells grown by molecular beam epitaxy with and without superlattice cladding layers are obtained with photoluminescence time-decay measurements. The authors show that superlattice layers reduce the interfacial recombination velocity from 330 cm/s, the value for double heterostructures with alloy cladding layers, to 40 cm/s, and that they have small effect on the GaAs bulk lifetime.

High-quality AlGaAs/GaAs quantum well with a short period (InGaAs)(GaAs) strained superlattice buffer layer

The optical quality of AlGaAs/GaAs single quantum wells prepared by MBE has been remarkably improved by the introduction of an (InGaAs)(GaAs) strained superlattice buffer (SSLB) layer and an AlGaAs/GaAs superlattice buffer (SLB) layer. The PL measurement shows more than 5 times higher peak intensity compared with that of the SLB alone. A GRIN-SCH single quantum well 770 nm laser with both SSLB and SLB was also examined. A high internal quantum efficiency of 95% with a small cavity loss of α = 3cm -1 and a high differential quantum efficiency of 50% even for a 3200 μm long cavity have been achieved.

High-efficiency AlGaAs/GaAs single-quantum-well semiconductor laser with strained superlattice buffer layer

The use of a strained superlattice buffer (SSLB) layer composed of a short-period (InGaAs)(GaAs) superlattice in a lattice-matched AlGaAs/GaAs system in order to reduce the internal stress is discussed. A five-times-higher photoluminescence peak intensity has been observed from a single quantum well (SQW) with the SSLB than without the SSLB. A high-quantum efficiency, a small cavity loss, and high-output power operation have been achieved in a narrow ridge-waveguide 770-nm graded-index-separate confinement heterostructure SQW laser diode with the SSLB. >

Misfit stress relaxation phenomena in GaAsP-InGaAs strained-layer superlattices

Misfit stress relaxation phenomena were investigated in InGaAs-GaAsP strained-layer superlattice layers as a function of period thickness using x-ray diffraction topography and electron-beam-induced current techniques. By controlling the thickness of the individual layer, as well as the total thickness of an InGaAs/GaAsP strained-layer superlattice, we have achieved a defect density reduction in GaAs epilayers grown on GaAs substrates. Several strained-layer superlattice buffer layers whose period thickness varied from 80 to 120 nm have been studied.

High-performance Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation-doped field-effect transistors prepared by molecular-beam epitaxy

High‐performance Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation‐doped field‐effect transistors (MODFET’s) have been further improved by replacing the Al0.48In0.52As buffer layer with an Al0.55In0.45As/Al0.41In0.59As strained‐layer superlattice (SLS) buffer layer, grown lattice matched to InP substrate by molecular‐beam epitaxy (MBE). Extrinsic transconductance as high as 306 mS/mm at 300 K has been obtained along with complete pinch off behavior for 1.7 μm gate length devices. This is attributed to the dislocation filtering and impurity gettering effects of the Al0.55In0.45As/Al0.41In0.59As SLS. Structural characterization using double crystal x‐ray diffraction also reveals the high quality of this SLS buffer layer.

Dislocation-free GaAs epitaxial growth with the use of modulation-doped AlAs-GaAs superlattice buffer layers

Suppression of dislocation threading from the substrate into GaAs epitaxial layers is investigated by using AlAs-GaAs superlattice buffer layers grown by molecular beam epitaxial technique. The efficiency of suppression is compared among several types of AlAs-GaAs superlattices with different electrically active impurity-doping distributions. With the use of modulation-doped AlAs(Si)-GaAs superlattice, dislocation threading is almost perfectly suppressed, and consequently, a dislocation-free epilayer can be grown. Dislocation bending at the AlAs/GaAs interface is thought to be due to the interaction between dislocations and electric charges.

Molecular beam epitaxial growth and characterization of ZnTe and CdTe on (001) GaAs

Investigations of elemental diffusion in (001) and (111) oriented CdTe and ZnTe layers grown by molecular beam epitaxy on (001) GaAs substrates show high Ga diffusion along dislocations and defects generated at the substrate-epilayer interface. The use of CdTe/ZnTe superlattice buffer layers and nucleation on near-atomically planar GaAs surfaces is shown to suppress Ga diffusion to background detection levels.

Epitaxial growth of InP on Si by OMVPE — defect reduction in epitaxial InP using InAsxP1−xInP superlattices

The heteroepitaxy of InP on Si substrates was investigated using OMVPE. A new epitaxial structure with a GaAs intermediate layer, 100 nm thick, was used to alleviate the 8.4% lattice mismatch between InP and Si. Four-inch size InP single crystal with a specular surface and good thickness uniformity (Δdd=±8%) was reproducibly obtained. It was found that the GaAs intermediate layer effectively reduced the residual stress in the InP epilayer and 8.4×108 dyn/cm2 was obtained. The EPD of the as-grown epilayer, etched by HBr+H3PO4 solution, was on the order of 108 cm−2 and it decreased to (2−4)×107 cm−2 by post growth annealing in PH3+PH2 ambient. To further reduce crystalline defects, a buffer layer consisting of ten periods of InAsxP1−x(2.5 nm)InP(2.5 nm) was formed between the InP epilayers grown on both as-grown and annealed InP/GaAs/Si substrates (x=0.3). This superlattice buffer layer reduced the EPD of these epilayers to 30–50%. Using a stacked structure with superlattice buffer layer and annealed InP/GaAs/Si substrate, an InP epitaxial layer with EPD of 1×107 cm−2 was obtained.

Structural properties of GaAs-on-Si with InGaAs/GaAs strained-layer superlattice

This paper investigates structural properties of GaAs epitaxial layers formed with an in-situ thermal cycle (TC) process and/or in InGaAs/GaAs strained-layer superlattice (SLS) buffer layer. Surface etch pit density (EPD) and cross-sectional transmission electron microscopic observation show that in-situ TC followed by SLS buffer layer growth effectively reduces threading dislocations on the order of 106 cm−2 for 3.5 μm thick epilayers. The degree of reduction strongly depends on the SLS structure and the number of in-situ TC cycles. EPD profiles for in-situ TC samples with and without SLS buffer show that the SLS buffer reduces threading dislocations in the regions both above and below the SLS. This may be because SLS-induced strain, caused by lattice mismatch between the SLS layer and the underlying GaAs layer, bends and thereby reduces threading dislocations in this underlying layer. An observed PL peak shift in the underlying layer due to incorporation of the SLS buffer supports this interpretation. It is also found that the optimum InxGa1−xAs/GaAs SLS structure is one whose total thickness is 2–10 times greater than the calculated critical thickness for the average composition 〈x〉 of the SLS buffer.

Effectiveness of strained-layer superlattices in reducing defects in GaAs epilayers grown on silicon substrates

In GaAs-GaAsP strained-layer superlattices grown lattice matched to GaAs are effective buffer layers in reducing dislocations in epitaxial GaAs films grown on Si substrates. The strained-layer superlattice structure permits high values of strain to be employed without the strained-layer superlattice generating dislocations of its own. We find that the strained-layer superlattice buffer is extremely effective in blocking threading dislocations of low density and is less effective when the dislocation is high. It appears that for a given strained-layer superlattice there is a finite capacity for blocking dislocations. Transmission electron microscopy has been used to investigate the role of the superlattice buffer layer.

Photoluminescence microscopy of epitaxial GaAs on Si

We report microscopic photoluminescence images and corresponding spectra of epitaxial GaAs on Si substrates, prepared by molecular beam epitaxy. High magnification (3000×) images directly reveal dislocations present in the epilayer. Several substrate orientations are investigated including nominal (001) tilted 4° toward 〈110〉. The GaAs samples include structures grown with and without superlattice buffer layers. Some samples were annealed at several temperatures from 650 to 850 °C. The dislocation density versus depth is studied by varying the optical probe wavelength and by studying samples that had been beveled and etched. In addition, the images and spectra are studied over a wide temperature range.

Effect of compositionally graded and superlattice buffer layers on the device performance of graded barrier quantum well heterostructure laser diodes

The device performance of graded barrier quantum well laser diodes with various buffer layer structures grown by metalorganic chemical vapor deposition has been studied. Devices having four structures (a GaAs buffer layer only, a compositionally graded buffer layer, a superlattice buffer layer, or both a graded and a superlattice buffer layer) have been characterized. In contrast with similar studies involving laser devices grown by molecular beam epitaxy, little variation in device performance is observed. These data indicate that the quality of AlGaAs-GaAs heterostructures for optical devices may be dependent on the details of the method used for the epitaxial growth of the layers.

GaInAs PIN photodiodes grown on silicon substrates for 1.55 μm detection

We report the first GalnAs PIN photodiodes to be fabricated on silicon substrates. Superlattice buffer layers were used to accommodate the lattice parameter mismatch. Reverse leakage currents of ̃70nA at – 1 V bias were measured for 105μm-diameter mesa diodes. The uncoated external quantum efficiency at a wavelength of 1.55μmwas 30%.

Defect Reduction in GaAs Epilayers on Si Substrates Using Strained Layer Superlattices

ABSTRACTInxGa11-xAs-GaAsl-yPy strained layer superlattice buffer layers have been used to reduce threading dislocations in GaAs grown on Si substrates. However, for an initially high density of dislocations, the strained layer superlattice is not an effective filtering system. Consequently, the emergence of dislocations from the SLS propagate upwards into the GaAs epilayer. However, by employing thermal annealing or rapid thermal annealing, the number of dislocation impinging on the SLS can be significantly reduced. Indeed, this treatment greatly enhances the efficiency and usefulness of the SLS in reducing the number of threading dislocations.

Tem Investigation of Strain Relaxation in ZnSe/ZnSxSe1−x Superlattices Grown by MBE

ABSTRACTThe relaxation mechanisms of ZnSe/ZnSxSe1−x superlattices grown by molecular beam epitaxy was studied by transmission rAeclmn icroscopy. The relaxation of misfit strain occured in part by conventional misfit dislocations that reside in the superlattice-buffer layer interface and in part by dislocations pinned at individual layer interfaces of the superlattice. The generation of misfit dislocations at the superlattice-buffer layer interface is inhibited by the misfit strain between individual superlattice layers. Therefore a significant amount of overall strain is present even after 1 μm of growth. Because misfit dislocations are not sufficient in relief of the misfit strain cracks are able to propagate

Defect reduction in GaAs grown by molecular beam epitaxy using different superlattice structures

Several superlattice structures, grown by molecular beam epitaxy, have been used to reduce the density of threading dislocations originating from the GaAs substrate. Results clearly indicate that compared to epitaxial layers grown directly on GaAs substrates, a GaAs-InxGa1−xAs superlattice (x<0.12) reduces the dislocations by approximately two orders of magnitude. Transmission electron microscopy, electron beam induced current, and etch pit density have been used to characterize the effectiveness of using superlattice buffer layers for the reduction of defects in GaAs epilayers.

Summary Abstract: Growth of device-quality GaAs and (Al,Ga)As on (211)-oriented silicon substrates, with thin (0.1 μm) superlattice buffer layers

Summary Abstract: Growth of device-quality GaAs and (Al,Ga)As on (211)-oriented silicon substrates, with thin (0.1 μm) superlattice buffer layers