H. Q. Hou

Organometallic vapor phase epitaxy (OMVPE)

Abstract Organometallic vapor phase epitaxy (OMVPE) has emerged in this past decade as a flexible and powerful epitaxial materials synthesis technology for a wide range of compound–semiconductor materials and devices. Despite its capabilities and rapidly growing importance, OMVPE is far from being well understood: it is exceedingly complex, involving the chemically reacting flow of mixtures of organometallic, hydride and carrier-gas precursors. Recently, however, OMVPE technologies based on high-speed rotating disk reactors (RDRs) have become increasingly common. As fluid flow in these reactors is typically cylindrically symmetric and laminar, its effect on the overall epitaxial growth process is beginning to be unraveled through quantitative computer models. In addition, over the past several years, a combination of well-controlled surface science and RDR-based growth-rate measurements has led to a richer understanding of some of the critical gas and surface chemistry mechanisms underlying OMVPE. As a consequence, it is becoming increasingly possible to develop a quantitative and physically based understanding of OMVPE in particular chemical systems. In this article, we review this understanding for the important specific case of AlGaAs OMVPE in an RDR under conditions used for growing typical device heterostructures. Our goal is to use typical growth conditions as a starting point for a discussion of fundamental physical and chemical phenomena, beginning with the fluid flow through an RDR and ending with the chemical reactions on the surface. By focusing on one particularly important yet relatively simple specific case, this review differs from more comprehensive previous reviews. Viewed as a case study, though, it complements these previous reviews by illustrating the wide diversity of research that is related to OMVPE. It can also serve as a good starting point for the development and transfer of insights into other more complex cases, such as: OMVPE of materials families containing Sb, P or N species, of other devices types, and in other more complex reactor geometries.

Highly uniform and reproducible vertical-cavity surface-emitting lasers grown by metalorganic vapor phase epitaxy with in situ reflectometry

Vertical-cavity surface-emitting lasers (VCSELs) were grown by metalorganic vapor phase epitaxy. Excellent uniformity of Fabry-Perot cavity wavelength for VCSEL materials of /spl plusmn/0.2% across a 3-in diameter wafer was achieved. This results in excellent uniformity of the lasing wavelength and threshold current of VCSEL devices. Employing pregrowth calibrations on growth rates periodically with an in situ reflectometer, we obtained a run-to-run wavelength reproducibility for 770- and 850-nm VCSELs of /spl plusmn/0.3% over the course of more than a hundred runs.

High-performance 1.06-μm selectively oxidized vertical-cavity surface-emitting lasers with InGaAs-GaAsP strain-compensated quantum wells

We present the first room-temperature continuous-wave operation of high-performance 1.06-/spl mu/m selectively oxidized vertical-cavity surface-emitting lasers (VCSELs). The lasers contain strain-compensated InGaAs-GaAsP quantum wells (QWs) in the active region grown by metalorganic vapor phase epitaxy. The threshold current is 190 /spl mu/A for a 2.5/spl times/2.5 /spl mu/m/sup 2/ device, and the threshold voltage is as low as 1.255 V for a 6/spl times/6 /spl mu/m/sup 2/ device. Lasing at a wavelength as long as 1.1 /spl mu/m was also achieved. We discuss the wavelength limit for lasers using the strain-compensated QWs on GaAs substrates.

In situ pre-growth calibration using reflectance as a control strategy for MOCVD fabrication of device structures

In situ normal incidence reflectance, combined with a virtual interface model, is being used routinely on a commercial metal organic chemical vapor deposition reactor to measure growth rates of compound semiconductor films. The technique serves as a pre-growth calibration tool analogous to the use of reflection high-energy electron diffraction in molecular beam epitaxy as well as a real-time monitor throughout the run. An application of the method to the growth of a vertical cavity surface emitting laser (VCSEL) device structure is presented. All necessary calibration information can be obtained using a single run lasting less than 1 h. Working VCSEL devices are obtained on the first try after calibration. Repeated runs have yielded ±0.3% reproducibility of the Fabry-Perot cavity wavelength over the course of more than 100 runs.

Uniform and high power selectively oxidized 8×8 VCSEL array

We report the uniform characteristics of an 8/spl times/8 individually addressable high power 850 nm VCSEL array. To achieve 2-dimensional array uniformity, both growth and fabrication uniformity issues must be considered. The VCSEL wafer is grown by metalorganic vapor phase epitaxy using an EMCORE reactor designed and calibrated for high growth uniformity. The distributed Bragg reflector (DBR) mirrors are composed of Al/sub 0.16/Ga/sub 0.84/As/Al/sub 0.94/Ga/sub 0.06/As layers with continuous compositional grading at the interfaces. In the 6 DBR periods on each side of the optical cavity the doping profile is decreased to as low as 5/spl times/10/sup 17/ cm/sup -3/ for reduced optical absorption. This design enhances the output power at the expense of relatively higher threshold voltage.

Monolithic wavelength-graded VCSEL and resonance-enhanced photodetector arrays for parallel optical interconnects

The key components in many wavelength-multiplexed optical interconnect architectures consists of monolithic arrays of uniformly-wavelength-graded optical sources and wavelength-selective photodetectors. These arrays can minimize optical crosstalk in a parallel free-space optical interconnect, increase the data throughput in a wavelength-multiplexed fiber channel, or enhance the functionality of an optical interconnect by providing wavelength-controlled optical routing. Multi-wavelength VCSEL arrays have been achieved by varying the thickness of only the active layer, which resulted in varying mirror losses and non-uniform device characteristics. We describe a wavelength-grading scheme that scales the thickness of all the layers within the resonance structure, which reduces the loss dispersion and improves device uniformity. We show that wavelength-graded arrays of VCSELs and resonance-enhanced photodetectors (REPDs) can be produced in a repeatable and uniform manner by controlling the local MOCVD growth rate of the epilayers on a topographically patterned substrate. We further show that wavelength-graded arrays of VCSELs and REPDs can be monolithically integrated on the same substrate, thus improving the wavelength matching between the source and detector arrays.