GaAs Multilayer Structures Research Articles

Highly reproducible tunnel currents in MBE-grown semiconductor multilayers

Tunnel currents through semiconductor tunnel barriers have proved very difficult to control to the extent that device-to-device variability and wafer-to-wafer irreproducibility have prevented electronic devices based on tunnelling from ever going into production. With reference to a single tunnel barrier of AlAs in a GaAs multilayer structure with an asymmetric doping profile, it is shown that, with careful attention to detail, diodes from equivalent sites on three separate wafers can be produced whose average current in forward bias is within 1 % while the total in-wafer standard deviation of current at the same fixed bias (0.5 V) is 6 %, dominated by a systematic cross-wafer variation that is described. This level of reproducibility now enables these devices to be used in pick-and-place systems for the manufacture of low-cost hybrid integrated microwave circuits.

Switching avalanche S-diodes based on GaAs multilayer structures

Results of studying volt-ampere characteristics of switching avalanche S-diodes are presented. It is shown that, for S-diodes based on structures obtained by diffusing Cr into GaAs, a larger part of the applied reverse-biased voltage drops across a high-resistance π-region but not across the space-charge region. In this case, the sharp increase of the current is caused by the electron injection from the forward-biased contact to the π-layer. In this respect, a new GaAs-based structure doped with Cr and Fe (GaAs:Cr, Fe) is studied. It is shown that, in S-diodes based on (GaAs:Cr, Fe)-structures, the current increase under a reverse bias is caused by avalanche processes in the space-charge area. This leads to producing a negative differential resistance section with subnanosecond switching from the closed to open state. The switching voltages of S-diodes on GaAs:Cr, Fe structures vary from 350 to 650 V, and the switching times do not exceed 0.5 ns.

Magneto-optical parameters of Co 90Fe 10 and Co 50Fe 50 ferromagnetic thin films for 1.3 μm integrated isolator

In order to optimize a 1.3 μm integrated optical isolator using a CoFe alloy for the non-reciprocal magneto-optical (MO) transverse Kerr effect, we have measured the optical and magneto-optical indices of Co 90Fe 10 and Co 50Fe 50 alloys grown in the Al 2O 3/Al/CoFe/GaAs multilayer structure. The optical reflectivity and MO rotation and ellipticity measurements were performed at variable incidence angle and s and p polarization of the incident light. In order to determine the optical and MO indices, the experimental data were fitted using a Matlab implementation of a standard multilayer Yeh formalism including multiple reflections. This original procedure allows precise determination of the optical and MO indices of CoFe alloys.

Determination of doping profiles on bevelled GaAs structures by Raman spectroscopy

A method for determination of doping concentration profiles of GaAs multilayer structures on a bevelled surface by Raman spectroscopy is presented. By scanning the laser beam along the bevel we obtained micro-Raman spectra in different depth positions in the structure. Calculated I TO/ I LO intensities determine the doping concentration in these points for values above 3×10 16 cm −3. The results are compared with electrochemical capacitance–voltage technique and secondary ion mass spectrometry. Some specific problems are discussed.

Electronic structure of (001) AlAs–InAs–GaAs multilayer structures

The electronic structure of different (001) (AlAs) m (InAs) 1(GaAs) n multilayer structures is studied. We have thus seen the influence of the relative thicknesses of the constituent materials and of the positions of the InAs principal layers in the multilayer structures on the energy eigenstates and on their spatial localization. The calculations are based on an sp 3s * empirical tight-binding model and on the surface Green function matching method.

Cross sectional Tem Sample Preparation Using E-Beam Lithography and Reactive ion Etching

AbstractA simple method to make cross sectional TEM samples of Si and GaAs semiconductor devices at specific device locations using electron beam (e-beam) lithography and reactive ion etching is described. The basic idea of this technique is to form pillar or line type patterns thin enough to be transparent to electron beams used in transmission electron microscopy. Since the entire process is conducted in the semiconductor fabrication facility, reliable samples were efficiently obtained within a short time without mechanical polishing or ion milling. High Resolution Electron Microscopy (HREM) images of SiGe and GaAs multilayer structures were obtained by this method. Using the alignment function of the e-beam lithography system, cross sectional TEM samples at specific locations of MOS transistors were obtained. The samples were thin enough to obtain HREM images of atomic level defects in the device.

Lattice-Matched InAsN(X=0.38) on GaAs Grown by Molecular Beam Epitaxy

AbstractIn this paper, we report the MBE growth of high nitrogen content lattice-matched InAs1−xNx (x=0.38) single crystal epitaxial films on GaAs. The nitrogen incorporation is about an order higher than previously reported on other mixed group V nitride alloys. These data are consistent with a nitrogen solubility limit calculation in various III-V binary alloys, which predicts orders of magnitude higher nitrogen incorporation in InAs than any other alloys. InAsN growths were obtained using a modified ECR-MBE system with atomic-nitrogen generated by an ECR plasma source. Improved crystal quality was obtained using a “template” growth technique. An x-ray linewidth of 270 arc-s was achieved on a 0.4 μm thick InAs0.62N0.38/GaAs multi-layer structure. Hall effect data show these InAsN films are semi-metallic.

Extremely flat surfaces by liquid phase epitaxy

By analysis of liquid phase epitaxial (LPE) growth experiments of GaAs multilayer structures, the incorporation rates at elementary growth steps (kinetic coefficients) are estimated. Conditions are presented to prepare large singular surfaces with several micrometers distances between regular elementary steps. Such quasi atomically flat surfaces may become important for applications in semiconductor and superconductor technologies, in surface physics and catalysis, as reference planes, and also as substrates for fabrication of extremely homogeneous layers and perfect superlattices.

Micro-Raman study of the residual stress in molecular-beam-epitaxy-grown Al xGa 1− xAs/GaAs multilayer structures

Extensive Raman-scattering investigations in the cleaved cross-sections of molecular-beam-epitaxy-grown Al x Ga 1− x As/ GaAs multilayer structures on GaAs or silicon substrates have been carried out by micro-Raman spectroscopy. The structures of the epitaxial layers are Al 0.3Ga 0.7As/Al 0.2Ga 0.8As/Al 0.1Ga 0.9As/GaAs (type A) and Al 0.1Ga 0.9As/Al 0.2Ga 0.8As/Al 0.3Ga 0.7As/GaAs (type B). The largest residual stress was observed in the Al 0.3Ga 0.7As layer of the type B structure on GaAs substrate and the value was estimated to be about 1.5 × 10 10 dyn cm −2 in the compressive mode. It was also found that the mode of the residual stress in the substrates differed according to the epitaxial structures grown on them. A model of residual stress in Al x Ga 1− x As/ GaAs multilayers grown on GaAs or silicon substrates is proposed: namely, if a substrate exists on the Al 0.1Ga 0.9As side, compressive stress acts on the substrate, and on the Al 0.3Ga 0.7As side, tensile stress acts.

Characterization of conducting GaAs multilayers by infrared spectroscopy at oblique incidence

The electrical and geometric properties of GaAs multilayer structures are measured nondestructively by infrared reflectance spectroscopy (50–5000 cm−1). Using oblique incidence and both s- and p-polarizations of the probing beam, carrier concentration and thickness of the epitactic films as well as the carrier concentration of the GaAs substrate are determined. The main structures in the spectra are due to phonon reststrahlen bands, Fabry-Perot interferences and the zeros of the dielectric function leading to dips in the reflectance (Berreman Mode). The results compare favorably with a depth-resolved secondary ion mass spectrometric (SIMS) sample analysis. The range of applicability of the method is discussed.

Metalorganic chemical vapor deposition and photoluminescence of nm GaAs doping superlattices

Metalorganic chemical vapor deposition of ultrathin doped GaAs multilayer structures is reported. Low-temperature photoluminescence is used as a powerful characterization method. By observing the shift of the effective band gap with varying layer thickness of doping superlattices we demonstrate that highly doped layers which are separated by only 4 nm do not diffuse together during growth.

Selective area MBE technique for GaAs coplanar diodes and GaAs SOI applications

The selective eptiaxy of GaAs multilayer structures through windows in SiO2 deposited on (001) oriented semi−insulating GaAs substrates for GaAs coplanar diodes, has been studied. It is shown that excellent flat, smooth, and straight boundaries of windows can be obtained by use of sidewall orientation with [1̄01] or [101] directions. GaAs coplanar diodes were fabricated by this technique. The characteristics of the polycrystalline GaAs grown on SiO2 (001)GaAs, SiO2-(100)Si, and SiO2-(111)Ge substrates have been examined by TEM, SEM, and x-ray diffraction. The results obtained show grain size of 1.0 to 3.3 μm can be achieved. The preferred orientation of the grains were [111], [400] and [800] for polycrystalline GaAs SOI on SiO2-(001)GaAs and [111] for polycrystalline GaAs SOI on SiO2-(100)Si and SiO2-(111)Ge.

Simple and rapid determination of carrier concentration and mobility profiles in GaAs

We describe a simple and fast method to obtain carrier concentration and Hall mobility profiles of GaAs multilayer structures on semi-insulating substrates from automatic van der Pauw-Hall measurements using a continuous chemical etching technique. In addition, a simplified procedure for determining conductivity profiles is presented. Applications to GaAs multilayer structures prepared by vapour phase epitaxy demonstrate the high depth resolution of these techniques.