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.

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 “cat's 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.

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 MOCVD's 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.

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.

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°.

The flow pattern of process gas at atmospheric pressure in a rectangular cross-section, horizontal MOCVD reactor was determined by pyrolyzing trimethylindium to produce an indium "smoke." Growth tubes with 9cm and 30cm entrance lengths and various internal geometries were tested. Entrance effects dominated the flow behavior for all tubes tested. This behavior is not generally recognized but is predicted from entrance-length theory. Use of a gas diffuser positioned slightly upstream from the susceptor produced no visible backflow of pyrolyzed reagent while greatly improving uniformity of flow over the susceptor. Im-proved control over GaAs film growth was obtained using a diffuser. These results lead to an improved design for a horizontal MOCVD reactor growth tube.