Eric S. Johnson

Fabrication and characterization of InGaP/GaAs heterojunction bipolar transistors on GOI substrates

In this letter, we report the first demonstration of InGaP/GaAs heterojunction bipolar transistors (HBTs) on germanium-on-insulator (GOI) substrates. We have performed physical characterization of the epitaxial layers to verify the high quality of the III-V epitaxial material grown on the GOI substrates and performed dc characterization of large-area InGaP/GaAs HBTs fabricated on the substrates. The InGaP/GaAs HBTs realized on GOI substrates were compared with identical devices grown on bulk germanium substrates and similar devices on semi-insulating GaAs substrates.

Critical misorientation morphology in AlGaAs and GaAs grown by atmospheric-pressure MOCVD on misoriented substrates

Abstract Critical misorientation morphology has been observed in AlGaAs epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) for the first time. These observations may lead to smoother epitaxial layers grown by MOCVD. Misorientation effects were previously observed in both liquid phase epitaxy (LPE) and chloride-transport vapor phase epitaxy growth of GaAs. More recently, molecular beam epitaxy grown AlGaAs deposited on substrates critically misoriented from (100) at growth temperatures below 700°C resulted in atomically-smooth morphology and improved photoluminescence compared to similar epitaxial films grown on nominally (100)-oriented substrates. This work describes a study of misorientation effects in the growth of AlGaAs and GaAs by atmospheric-pressure MOCVD. The pronounced rough morphology reported here was observed at 700°C using misoriented (100) GaAs substrates with a high density of induced nucleation flaws. Growth on these substrates was characterized by faceted defects with a well-defined angle between singular-plane treads and clustered monatomic step risers. These faceted defects were not formed when the substrate misorientation reached an angle of 2.5°−3.0° from the (100). Long-range morphology on a GaAs epitaxial layer in the form of terraces similar to those seen in LPE was also observed for growth at 700°C on a well-prepared (100) substrate. The observation of long-range surface morphology and critical misorietation effects demonstrates that near-equilibrium growth conditions have been found in atmospheric-pressure MOCVD where the step surface energy is lowered by a long-range morphology of treads and risers, for growth on slightly misoriented (100) substrates.

InGaP PHEMTs for 3.5GHz W-CDMA applications

In this paper we present DC, small signal, and power characteristics of an InGaP PHEMT device using InGaP as barrier layer material. A comparison of intrinsic Gm, Rds, Cgs, and Cgd with an AlGaAs PHEMT device showed that the InGaP PHEMT is very promising for microwave and RF linear power amplification. Operating from 12 V supplies, a 15.4 mm InGaP PHEMT device achieved 29.5 dBm output power with 12.1 dB associated gain and 25.6% power-added-efficiency at 3.5 GHz, while meeting the -40 dBc ACPR specification under W-CDMA stimulus.

A MOCVD reactor safety system for a production environment

Abstract MOCVD growth of GaAs frequently is accomplished using trimethylgallium and arsine. Although these materials are presently used safely worldwide in a research environment, their hazardous nature is an important consideration in the application of MOCVD to production. This paper describes a MOCVD reactor safety-interlock and automatic shutdown system now being evaluated on a research reactor for its suitability in a production environment. Some specific features employed are fire detection, reactor overpressure prevention, and toxic gas exposure control. This paper will also discuss the technique used to remove As and AsH 3 from the reactor exhaust.

Growth of AlGaAs and GaAs by atmospheric-pressure MOCVD on lenticular substrates

Abstract Critical orientation effects are well known in epitaxial layers grown by VPE and LPE. More recently, effects have been observed in rough growth in MBE-grown AlGaAs and as faceted morphology and terraces in MOCVD-grown AlGaAs and GaAs. For the case of growth by LPE and MBE, a critical misorientation unique to the growth conditions resulted in a smoothening of rough or terraced growth morphology. In addition, MBE-grown AlGaAs deposited on lens-shaped substrates at growth temperatures below 700 °C resulted in atomically smooth morphology and improved photoluminescence (PL) spectra for substrate areas having a critical misorientation toward the nearby (111)A planes, whereas the epitaxial films grown elsewhere (including the nominally (100)-oriented center of the substrate) were rough and had poor quality PL. This work describes a study of the growth by atmospheric-pressure MOCVD at 650–700 °C of AlGaAs and GaAs on lens-shaped substrates which sample surface misorientations up to 22° from the (100). Only visually smooth growth and no change in the band-edge PL wavelength were observed for small misorientations from the (100) plane under these growth conditions, in contrast to readily observed rough morphology patterns and PL band-edge shifts in MBE. Patterns of rough growth due to microscopic point defects associated with specific crystalline orientations were observed for both MOCVD-grown AlGaAs and GaAs films for surface misorientations greater than 10°.

Strong enhancement of band edge PL intensity and improved morphology for AlGaAs grown on lenticular GaAs substrates by low pressure MOVPE

Abstract It is widely known that the band edge photoluminescence (PL) intensity of MOVPE-grown AlGaAs decreases rapidly below that of comparable LPE-grown material for MOVPE growth temperatures below 780°C. This paper demonstrates that most of the lost intensity can be recovered in low pressure (LP) MOVPE by the use of a high substrate misorientation from {100}. AlGaAs (25% Al) was grown at 700°C on a GaAs lenticular substrate at 30 Torr. PL spectra for the AlGaAs film were taken as a function of substrate misorientation. The band edge intensity was found to be strongly misorientation dependent, with minimum intensity at 2° –3° of misorientation (a commonly used MOVPE misorientation) and maximum intensity at greater than 10° of misorientation. The maximum to minimum intensity ratios were 1000 at 77 K and 50 at 300 K. AlGaAs grown at a misorientation of 2°-3° or less had moderate band edge intensity with considerable deep level emission, whereas at high misorientation only band edge emission was observed. The 300 K PL intensity enhancement of 50-fold with high misorientation is approximately what is lost in reducing the growth temperature (700°C versus 780°C) on nominal {100} substrates using conventional TMGa, TMAl and arsine sources. These results suggest that AlGaAs with high optical quality can be grown at reduced growth temperatures by LP MOVPE if high substrate misorientations are employed. This paper also reports the observation of extended regions of {100} facets with dimensions on the order of a micron for AlGaAs grown on a GaAs lens by LP MOVPE. The regions of long-range morphological ordering appear as a “cats eye”-shaped feature and for representative growth conditions cover the area with misorientation less than 4.5° from {100}. The long-range ordering in morphology does not appear to originate from nucleation flaws, a case reported previously for atmospheric pressure MOVPE.

An 8-Watt 3.5 GHz power amplifier with tunable matching

A high power 3-stage, S-band power amplifier MMIC implemented with a partially matched output stage is presented. This MMIC PA achieves 39 dBm output power and greater than 25% power added efficiency using 0.6 /spl mu/m PHEMT technology. Small-signal performance matches very well with modeled predictions. The amplifier is exceptionally stable under varying loads, has a bandwidth of several 100 MHz and is easily matched and tuned about the 3.5 GHz band with a simple output matching technique using chip caps, bond wires and duroid transmission lines.

Filling of light emitting diode via-holes by MOCVD

The growth of epitaxial films on featured substrates has an important device application in junction-confinement, double hetero-structure light emitting diodes. These devices are presently grown by a liquid phase epitaxy process but growth by metalorganic chemical vapor deposition is desirable because of MOCVDs superior surface quality, uniformity, and throughput. This paper describes the effect of growth parameters on AlGaAs films deposited by atmospheric-pressure MOCVD into substrate holes typically made in the fabrication of junction-confinement LEDs. MOCVD growth replicates the substrate features; it does not give a planar surface over the holes. The behavior of epitaxy filling into holes is strongly dependent on growth temperature and total gas flow and largely independent of substrate misorientation and the thickness of the layer grown. Wet-etched holes formed (ll0)-oriented V-groove and dovetail-groove features on the hole circumference. Faceting of the MOCVD growth was seen on the wall with the (111)A feature while smooth growth was seen on the etched (111)B surface.

Evaluations of a Commercially Available Electrical Probe

The demands of submicron VHSIC Technology are trending to + .10 pm critical dimension control and + .10 μm overlay control. Equipment such as that evaluated in this paper will take an increasing role in this environment because it offers precision in the .002 μm range 1 a, moreover it produces the required data base in a reasonable time. The electrical prober provides alignment and linewidth data from specialized test structures etched into conductive films. This can provide a wealth of information about the photo/etch process. Again, it must be emphasized that the data collection process is highly automated and, therefore, very objective. In this paper, summaries of evaluations performed on various types of lithographic equipment available to us are presented. Processes used to generate the test structures are shown. Applications of the modeling capabilities when applied to the lithographic equipment are also included. This system can be very useful, for example, when applied to a projection 1:1 scanning system. One can model for translation and rotation error, commonly induced by operator misalignment, and thereby separate it from typical equipment related problems, i.e., scan, crosscan. The system will also model lens distortions and stepping errors from data accumulated with step-and-repeat equipment. Vector mapping of misregistration and contour mapping of linewidth variation gives one a powerful tool for seeing his own process capabilities. Comparison testing of the electrical prober to other linewidth measuring equipment, including optical and SEM, will also be reviewed. This is very important as linewidth measurement is fundamental to the electrical probers operation. Optical systems for linewidth measurement and verniers placed directly on product provide a fine front line in baselining a process, particularly because of their immediate feedback of good data (bad sources notwithstanding). But, the process engineer using the electrical prober will realize a data base that truly enables him to make definitive statements about his own process as more stringent device requirements present themselves.