John A. Lebens

Application of selective epitaxy to fabrication of nanometer scale wire and dot structures

The selective growth of nanometer scale GaAs wire and dot structures using metalorganic vapor phase epitaxy is demonstrated. Spectrally resolved cathodoluminescence images as well as spectra from single dots and wires are presented. A blue shifting of the GaAs peak is observed as the size scale of the wires and dots decreases.

Direct determination of the ambipolar diffusion length in GaAs/AlGaAs heterostructures by cathodoluminescence

A new technique for determining carrier diffusion lengths by cathodoluminescence measurements is presented. The technique is extremely accurate and can be applied to a variety of structures. Ambipolar diffusion lengths are determined for GaAs quantum well material, bulk GaAs, Al0.21Ga0.79As, and Al0.37Ga0.63As. A large increase in the diffusion length is found for Al0.37Ga0.63As and is attributed to an order of magnitude increase in lifetime.

Selective epitaxy of GaAs, AlxGa1−xAs, and InxGa1−xAs

Abstract Many device structures benefit from the ability to selectively deposit epitaxial materials. Through the use of a masking material, such as Si3N4 or SiO2, on the substrate surface, patterns generated through standard lithographic procedures can be used to define regions for selective deposition. Highly selective growth can be achieved through the use of growth precursors which contain halogens, such as (C2H5)2GaCl and (C2H5)2AlCl. These compounds decompose, most probably, to the volatile mono-halogen species, e.g. GaCl, and also generate HCl in the gas phase as a reaction by-product. We present experimental results on the morphology and growth behavior of GaAs, AlxGa1−xAs, and InxGa1−xAs using this selective epitaxy technique. Electri cal and optical characterization has been carried out on these materials and selectively grown structures produced by this technique. The interface between the selectively grown material and the underlying substrate was investigated and the conditions for achieving high quality electrical interfaces were determined. A thermodynamic model of this growth chemistry predicts the trends in composition and growth rate. The thermodynamic model, based on the quasi-equilibrium of the halogen-based compounds with the substrate surface, indicates that the growth behavior is very similar to the inorganic-based growth of these compounds. Experimental applications of this technique to high speed digital device structures and sub-micron dimensioned optical structures are presented.

Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1−xAs

The ambipolar diffusion length and carrier lifetime are measured in AlxGa1−xAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented.

Facet modulation selective epitaxy–a technique for quantum-well wire doublet fabrication

The technique of facet modulation selective epitaxy and its application to quantum-well wire doublet fabrication are described. Successful fabrication of wire doublets in the AlxGa1–xAs material system is achieved. The smallest wire fabricated has a crescent cross section less than 140 A thick and less than 1400 A wide. Backscattered electron images, transmission electron micrographs, cathodoluminescence spectra, and spectrally resolved cathodoluminescence images of the wire doublets are presented.

Preferential incorporation of defects in monocrystalline diamond films

Abstract Cathodoluminescence (CL) spectroscopy and microscopy and Raman scattering measurements of homoepitaxial diamond films, grown at substrate temperatures of 900 and 1200°C by microwave plasma-assisted chemical vapor deposition, reveal the preferential incorporation of defects in films grown on the (111) and (320) faces of diamond substrates compared with those grown on the (001) faces. The CL features observed include the broad bands centered at around 440 nm (2.82 eV) and 550 nm (2.25 eV) and a narrow band at about 740 nm (1.675 eV). The diamond films grown on the (111) faces exhibit strong non-uniformities in the distribution of impurities ( e.g. Si) and defects. The distribution of the 550 nm and 740 nm bands can be correlated with the topographic features in these films. The diamond films grown on the (001) faces show no 550 nm and 740 nm bands, and high-quality regions exhibit uniform monochromatic (440 nm) CL images.

Nanometer scale wire structures fabricated by diffusion‐induced selective disordering of a GaAs(AlGaAs) quantum well

A shallow zinc diffusion technique is used to selectively disorder a GaAs quantum well creating nanometer scale wire structures. Spectrally resolved cathodoluminescence images of the structures are presented as well as local spectra of cathodoluminescence emission from the structures. Blue shifting of the luminescence from the wire structures is observed.

A novel technique for the direct determination of carrier diffusion lengths in GaAs/AlGaAs heterostructures using cathodoluminescence

A novel technique for determining carrier diffusion lengths in direct gap semiconductors by cathodoluminescence measurement is presented. Ambipolar diffusion lengths are determined for GaAs quantum-well material, bulk GaAs, and Al/sub x/Ga/sub 1-x/As with x up to 0.38. A large increase in the diffusion length is found as x approaches 0.38 and is attributed to an order-of-magnitude increase in lifetime.<<ETX>>

Quantitative measurement of the composition of AlxGa1−xAs heterostructures using a simple backscattered electron detector

We describe a technique for the quantitative measurement of composition in Al_xGa_(1−x)As heterostructures using a simple solid‐state backscattered electron detector in a scanning electron microscope. Calibration data are presented and are shown to be consistent with the Castaing [Adv. Electron. Electron Phys. 13, 317 (1960)] theory. The technique is applied to image representative Al_xGa_(1−x)As heterostructures including a graded index separate confinement heterostructure (GRINSCH) laser structure.

Quantum wire and quantum dot semiconductor lasers

There is currently great interest in fabrication of structures that are two and three dimensional analogs of the conventional quantum well. We review here the physics behind the use of arrays of such lower dimensional structures in semiconductor laser active layers. Methods which are currently under investigation for producing such structures will be discussed.