Carrie Carter-Coman

ANALYSIS OF IN0,07GA0,93AS LAYERS ON GAAS COMPLIANT SUBSTRATES BY DOUBLE CRYSTAL X-RAY DIFFRACTION

Double crystal x-ray diffraction data is presented from the most extensive compliant substrate experiment to date. Five consecutive InGaAs–GaAs growths were performed simultaneously on GaAs-based thin film compliant substrates and thick reference substrates. The In0.07Ga0.93As layers were grown to thicknesses below and above the conventional critical thickness. It was found that InGaAs films grown on the compliant substrates have a larger critical thickness and slower strain relief than InGaAs grown on conventional GaAs substrates.

Growth of GaN on lithium gallate substrates for development of a GaN thin compliant substrate

Since we have found that an entire substrate can be chemically removed in less than 5 min and since GaN is impervious to chemical etching, the GaN on lithium gallate (LGO) system is an excellent template (due to near infinite etch selectivity) for developing a thin film/compliant GaN substrate. Here we report on our efforts to grow GaN on LGO, including improvement of the atomic surface morphology using pregrowth pretreatments. We also report the first transferred thin film GaN substrate grown on LGO, transferred off of LGO and mounted on GaAs. With this approach, (InAl)GaN alloys can be grown on thin GaN films, implementing a “compliant” substrate for the nitride alloy system. In addition, the flexibility of bonding to low cost Si, metal or standard ceramic IC packages is an attractive alternative to SiC and hydride vapor phase epitaxy GaN substrates for optimizing cost verses thermal conductivity concerns. We have demonstrated high quality growth of GaN on LGO. X-ray rocking curves of 145 arcsec are sho...

Strain‐modulated epitaxy: A flexible approach to 3‐D band structure engineering without surface patterning

Thin compliant growth substrates have been used to reduce the strain in lattice‐mismatched overlayers during epitaxial growth. This letter reports a new thin compliant substrate technology which allows these thin substrates to be patterned on the bottom, bonded surface. This lateral strain variation (inverted stressor) in the growing film can be combined with the additional effects of strain‐dependent growth kinetics to realize the lateral control of composition and thickness without any surface topography on the substrate. Initial demonstrations of the growth of InGaAs on GaAs bottom‐patterned thin substrates are presented herein.

Analysis of GaAs Substrate Removal Etching with Citric Acid : H 2 O 2 and NH 4 OH : H 2 O 2 for Application to Compliant Substrates

New properties associated with selective substrate removal have been observed in the application of this technique to GaAs thin film compliant substrates. Citric acid- and NH 4 OH-based etches are used to selectively etch the GaAs substrate and stop on an AlAs layer. The AlAs stop-etch layer is transformed into a layer that is almost twice as thick as the original layer, mismatched to the remaining GaAs epilayer, and has a refractive index around 2.0. Replacement of the single AlAs stop etch layer with multiple thin AlGaAs stop etch layers is proposed to alleviate this problem.

Metastability modeling of compliant substrate critical thickness using experimental strain relief data

A metastability model for GaAs compliant substrates is developed using the compliant substrate partitioning formula and experimental strain relief data. The developed model agrees with compliant substrate strain relief data deduced from double crystal x-ray diffraction and indicates that, for a set of growth conditions and compliant substrate thicknesses, layers of InGaAs of any thickness can be grown free of dislocations. The model developed in this letter is also compared to other compliant substrate critical thickness models, and the authors discuss the mechanisms of partitioning in mismatched layers grown on compliant substrates.

A new mechanism for spontaneous nanostructure formation on bottom-patterned compliant substrates

Bottom-patterned compliant substrates can be used to laterally modulate the properties of a mismatched epilayer. At temperatures where strain-dependent growth kinetics are significant, the GaAs bottom pattern compliant substrates affected the growth of strained InGaAs epilayers by causing lateral modulation in material height. Spatially aligned mounds and quantum dots were observed on the samples grown at high temperatures. A new mounding mechanism was observed on InGaAs layers grown on the compliant substrates. Strain-dependent growth kinetics and the bottom patterned compliant substrate are used to explain these effects.

Strain‐modulated epitaxy: Modification of growth kinetics via patterned, compliant substrates

Bonded, thin film compliant substrates can be used to reduce the strain in a lattice‐mismatched overlayer during epitaxial growth. We have presented an initial demonstration of the use of thin film GaAs compliant substrates fabricated by epitaxial liftoff or substrates removal and bonded to a mechanical host. This processing approach can be coupled with the patterning of the bonded surface to realize a lateral thickness variation. This thickness variation, in turn, can be used to realize a lateral strain variation in the growing mismatched overlayer. The strain can then be used to modify molecular beam epitaxy (MBE) growth kinetics, such as cation desorption and migration. With this technique the lateral control of composition and thickness can be realized without any surface topography. In this article, we discuss the growth of InGaAs films on compliant substrates produced by epitaxial lift‐off and substrate removal. In addition, we discuss the various extrinsic effects associated with the compliant subs...

Growth dynamics of InGaAsGaAs by MBE

The growth dynamics of the InGaAs/GaAs system have been investigated by desorption mass spectrometry (DMS). Indium desorption spectra indicate the presence of one or two desorption mechanisms depending on the V/III beam equivalent pressure ratio. The activation energy associated with one of the desorption processes is found to be 1.3 eV and independent of V/III ratio and arsenic species. Analysis of the decay curve allows the calculation of the indium surface population during growth. This population is compared for the different growth conditions investigated. Indium incorporation coefficient curves as a function of substrate temperature are presented. Indium incorporation is found to be enhanced using high V/III ratio and the arsenic dimer, As2.

Selective Wet Etching of Lithium Gallate

Lithium gallate (LGO) is an attractive, near lattice matched substrate for the growth of GaN. In addition, LGO substrates provide a convenient route to forming thin films of GaN as used in substrate removal or lift-off processes. We report the wet etching of LGO substrates for the production of GaN thin films. Two face-selective LGO etches have been used for the processing of substrates. The etch rate of the cation face is reported here for the first time and is 0.25 μm min -1 at 50°C. The etching solution is safe and benign to most materials including metallic bonding.