In situ monitoring of GaSb, GaInAsSb, and AlGaAsSb

Suitability of silicon photodiode detector arrays for monitoring the spectral reflectance during epitaxial growths of GaSb, AlGaAsSb, and GaInAsSb, which have cutoff wavelengths of 1.7, 1.2, and 2.3 {micro}m, respectively, is demonstrated. These alloys were grown lattice matched to GaSb in a vertical rotating-disk reactor, which was modified to accommodate near normal reflectance without affecting epilayer uniformity. By using a virtual interface model, the growth rate and complex refractive index at the growth temperature are extracted for these alloys over the 600 to 950 nm spectral range. Excellent agreement is obtained between the extracted growth rate and that determined by ex-situ measurement. Optical constants are compared to theoretical predictions based on an existing dielectric function model for these materials. Furthermore, quantitative analysis of the entire reflectance spectrum yields valuable information on the approximate thickness of overlayers on the pregrowth substrate

In-situ spectral reflectance for improving molecular beam epitaxy device growth

This report summarizes the development of in situ spectral reflectance as a tool for improving the quality, reproducibility, and yield of device structures grown from compound semiconductors. Although initially targeted at MBE (Molecular Beam Epitaxy) machines, equipment difficulties forced the authors to test most of their ideas on a MOCVD (Metal Organic Chemical Vapor Deposition) reactor. A pre-growth control strategy using in situ reflectance has led to an unprecedented demonstration of process control on one of the most difficult device structures that can be grown with compound semiconductor materials. Hundreds of vertical cavity surface emitting lasers (VCSEL`s) were grown with only {+-} 0.3% deviations in the Fabry-Perot cavity wavelength--a nearly ten-fold improvement over current calibration methods. The success of the ADVISOR (Analysis of Deposition using Virtual Interfaces and Spectroscopic Optical Reflectance) method has led to a great deal of interest from the commercial sector, including use by Hewlett Packard and Honeywell. The algorithms, software and reflectance design are being evaluated for patents and/or license agreements. A small company, Filmetrics, Inc., is incorporating the ADVISOR analysis method in its reflectometer product

Gas Chromatography-Mass Spectroscopy Study of tert-Butylarsine Stability and Purification

TBA (tert-butylarsine, H{sub 2}AsC(CH{sub 3}){sub 3}) has been demonstrated to be an effective arsenic precursor for the deposition of compound semiconductors such as GaAs by MOCVD (metal organic chemical vapor deposition). TBA is used as a liquid (bubbler) source in MOCVD and is a less toxic alternative to the more commonly used gaseous arsine (AsH{sub 3}). Materials and device performance using TBA have in many cases equaled or surpassed those using arsine. This includes the first observation of fractional quantum Hall behavior in a two dimensional electron gas structure grown by MOCVD. Despite the beneficial characteristics, the use of TBA in our laboratories has revealed some inconsistent behavior. Small pressure rises have been observed in the TBA bubbler sources when left unused over a period of many days. Measurements of the TBA partial pressure using UV absorption revealed that new absorption peaks could be observed after storage. The features of the absorption profile were insufficient to ascribe to a specific chemical species. Attempts to remove the gaseous impurities with liquid nitrogen freeze-pump-thaw techniques had limited success. Unfortunately, there is no published information on the room temperature decomposition of TBA. In this paper, we present a series of GCMS (gas chromatography-mass spectroscopy) analyses designed to determine the stability of TBA and identify its decomposition products in storage containers. The GCMS is also used to evaluate several methods for in-situ purification of TBA

In-Situ Monitoring of GaSb, GaInAsSb, and AlGaAsSb*

The suitability of the wavelength range provided by silicon photodiode detector arrays for monitoring the spectral reflectance during epitaxial growth of GaSb, AlGaAsSb, and GaInAsSb, which have cutoff wavelengths at 25 degree C of 1.7, 1.2, and 2.3 um, respectively, is demonstrated. These alloys were grown lattice matched to GaSb in a vertical rotating-disk reactor, which was modified to accommodate near normal reflectance without affecting epilayer uniformity, By using a virtual interface model, the growth rate and complex refractive index at the growth temperature are extracted for these alloys over the 600 to 1000 nm spectral range. Excellent agreement is obtained between the extracted growth rate and that determined by ex-situ measurement

In-situ monitoring of GaSb, GaInAsSb, and AlGaAsSb

Suitability of silicon photodiode detector arrays for monitoring the spectral reflectance during epitaxial growths of GaSb, AlGaAsSb, and GaInAsSb, which have cutoff wavelengths of 1.7, 1.2, and 2.3 {micro}m, respectively, is demonstrated. These alloys were grown lattice matched to GaSb in a vertical rotating-disk reactor, which was modified to accommodate near normal reflectance without affecting epilayer uniformity. By using a virtual interface model, the growth rate and complex refractive index at the growth temperature are extracted for these alloys over the 600 to 950 nm spectral range. Excellent agreement is obtained between the extracted growth rate and that determined by ex-situ measurement. Optical constants are compared to theoretical predictions based on an existing dielectric function model for these materials. Furthermore, quantitative analysis of the entire reflectance spectrum yields valuable information on the approximate thickness of overlayers on the pregrowth substrate

In-situ optical photoreflectance during MOCVD

This report summarizes the development of in situ optical photoreflectance as a tool for measuring impurity concentrations in compound semiconductors. The authors have successfully explored the use of photoreflectance as an in situ tool for measuring n-type doping levels in metal-organic chemical vapor deposition (MOCVD) grown GaAs materials. The technique measures phase and frequency shifts in Franz-Keldysh oscillations measured on uniformly doped thin films. Doping concentrations from 5 {times} 10{sup 16} to 1 {times} 10{sup 18} can be measured at temperatures below 130 C. A method has been developed to include photoreflectance as the last step in the pre-growth in situ calibration procedure for MOCVD thin film structures. This combined capability now enables one to rapidly and accurately determine growth rates, chemical composition, and doping levels necessary to generate a recipe to fabricate complex optoelectronic compound semiconductor devices