K.T. Shiralagi

In situ spectroscopic ellipsometry in molecular beam epitaxy

Noninvasive, real‐time material growth monitoring is becoming increasingly important as epitaxial layer structures become more complex and the thickness and alloy composition tolerances are reduced. The technique of spectroscopic ellipsometry has been adapted to a commercial III–V semiconductor molecular beam epitaxy (MBE) system to monitor layer thickness, ternary alloy composition, and substrate temperature in real time during the growth of multilayer structures. Practical system considerations for reliably implementing the rotating analyzer ellipsometer in a hydride source MBE environment that contains a high pressure of dimeric group V species will be discussed. Measurement of substrate temperature from room temperature to typical growth temperatures will then be presented as well as in situ determination of alloy composition and thickness for efficient growth calibration. A growth run of GaAs/AlGaAs epitaxial layers will be examined to observe surface smoothing upon group III pulse deposition and gro...

Electrical and optical characterization of gas source and solid source MBE low temperature buffers

MBE GaAs buffer layers grown at low substrate temperatures (200–300°C) have been shown to significantly reduce backgating and sidegating in GaAs integrated circuits. The isolation provided by these buffers is attributed to a high level of compensating traps in the layers induced by excess arsenic and arsenic antisite defects. Structures were grown by both gas source and solid source MBE in a VG Semicon V80H dual chamber system. The structures allow us to study characteristics of the LTB itself as well as the quality of active layers grown upon these buffer layers. The insulating characteristics of the gas and solid source LTBs are comparable. However, in contrast to control layers grown on semi-insulating GaAs, we observe considerably higher trap concentrations in FET active layers grown on LTBs. Deep level transient spectroscopy (DLTS) measurements show several resolvable electron and hole traps, plus a band of shallow hole traps. Due to the differences in growth kinetics for gas and solid source growth such a close similarity was not expected. The resistivity of the LTBs and the traps incorporated into the active layers appear to be similar for solid source (As4) and gas source (As2) growth. Furthermore, the characteristics of proximity annealed layers continue to change for varied length low temperature anneals. This indicates that the excess arsenic continues to diffuse into the active device layers degrading device stability.

Optical properties of a single strained InGaAs/GaAs quantum well grown on vicinal GaAs surfaces

We have studied the optical properties of single strained InxGa1−xAs/GaAs quantum wells (QWs) grown on GaAs substrates oriented off the (100) surface. Photoluminescence measurements indicate that QW structures grown on GaAs(100)5° toward (111)A possess superior interfaces as evidenced by the linewidth. There appears to be a decrease in the density of optically inactive traps as the angle of misorientation is increased, resulting in an enhanced optical efficiency at 77 K. However, these traps freeze out at 2 K and consequently, the optical efficiency of the various layers become independent of substrate orientation.

Real-Time Analysis Of In-Situ Spectroscopic Ellipsometric Data During Mbe Growth Of III-V Semiconductors

A modular spectroscopic ellipsometer, capable of both in-situ and ex-situ operation, has been used to measure important growth parameters of GaAs/AIGaAs structures. The ex-situ measurements provided layer thicknesses and compositions of the grown structures. In-situ ellipsometric measurements allowed the determination of growth rates, layer thicknesses, and high temperature optical constants. By performing a regression analysis of the in-situ data in real-time, the thickness and composition of an AIGaAs layer were extracted during the MBE growth of the structure.

Optical properties of strained asymmetric triangular InGaAs/GaAs multiple quantum wells

We present the first report of a strained‐layer asymmetric triangular In0.15Ga0.85As/GaAs multiple quantum well structure realized by molecular beam epitaxy. Low‐temperature photoluminescence experiments showed that the optical efficiency of such a structure is more than five times higher than an equivalent rectangular In0.15Ga0.85As/GaAs multiple quantum well structure grown under the same conditions. This is due to an increased collection of photoexcited carriers that are being swept by the well as a result of the field formed by compositional grading and a reduction of nonradiative recombination centers.

In-situ and ex-situ characterization of GaAs/AlAs quantum well structures using spectroscopic ellipsometry

Abstract Spectroscopic ellipsometer is used to monitor the MBE growth of quantum well structures. Real time monitoring of the growth enabled the measurement of growth rate and correlation with RHEED oscillations. The growth of a single GaAs/AlAs quantum well is also monitored in real time using multiple wavelengths. Interface roughness of the interrupted “inverted” AlAs/GaAs interface was also monitored with SE. Under our growth conditions, we measure approximately a 2 ML interfacial region at the inverted interface. A correlation with photoluminescence is also discussed.

Hydride cracker nozzle design for gas source molecular beam epitaxy

The design of a tantalum nozzle for group V hydride cells in gas source molecular beam epitaxy is presented. The nozzle, which determines the flux distribution from the group V cell is optimized for uniformity and maximum flux utilization. Arsine cracking efficiency and relative concentrations of various gas species are measured by a quadrupole mass analyzer. The operating temperature for the source cell is determined as the region where maximum dimeric arsenic is available for growth.

Low temperature GaAs grown by gas source molecular beam epitaxy

Abstract Low temperature growth of GaAs by gas source molecular beam epitaxy (GSMBE) is investigated. Reflection high energy electron diffraction is used to monitor the low temperature buffer (LTB) growth and anneal conditions. Growth at low temperatures with dimeric arsenic is more sensitive to the V/III flux ratios and substrate temperatures than with As 4 used in solid source MBE. Temperature dependent conductivity and deep level transient spectroscopy measurements are presented to observe trap outdiffusion from the LTB into subsequently grown FET channels. Low temperature photoluminescence spectra show degradation of quantum well properties when LTBs are grown with increasing V/III flux ratios.

A novel optical bistable multiple-quantum-well phase modulator

The authors present a new type of optically bistable phase modulator utilizing a self electrooptic effect device (SEED) integrated with an electrooptic wavelength modulator. An electrically bistable SEED, operating on the principle of the quantum-confined Stark effect, controls the bias voltage across an electrooptic waveguide phase modulator to produce optical bistability. A control signal at 0.848 mu m, corresponding to the first electron to heavy hole exciton transition in GaAs/AlGaAs multiple-quantum-well is used to switch 1.152 mu m light propagating through a waveguide in a direction normal to the control beam.<<ETX>>

Optical properties of quantum wells grown upon gas source molecular‐beam epitaxy low‐temperature buffers

GaAs/AlGaAs quantum wells are grown on gas source molecular‐beam epitaxy (GSMBE) grown low‐temperature buffers (LTB). Changes in LTB growth conditions produce noticeable changes in photoluminescence (PL) intensity and linewidths of the quantum wells. Layers grown at low temperatures (200–300 °C) incorporate excess arsenic which outdiffuses during subsequent quantum well growth. Reflection high energy electron diffraction and PL results are utilized to show strain and arsenic outdiffusion from the LTBs. Excess arsenic incorporation during the growth of GaAs at low temperatures is explained in terms of the association reaction of As2 to form As4 at the surface. The optimum V/ III ratio for growth of LTB by GSMBE is discussed.