A. Eisenbach

Improved quality GaN by growth on compliant silicon-on-insulator substrates using metalorganic chemical vapor deposition

The use of compliant silicon-on-insulator (SOI) substrates instead of Si substrates is shown to improve the quality of epitaxial GaN layers by releasing the strain and absorbing the generated threading dislocations in the thin Si overlay of the SOI substrate. GaN layers have been grown on SOI substrates by low-pressure metalorganic chemical vapor deposition and various growth conditions and compared with GaN layers grown on Si substrates. Crystal uniformity, surface morphology, and number of threading dislocations of GaN layers grown on SOI substrates are improved compared to layers grown directly on Si substrates as evidenced by x-ray diffraction spectroscopy (XRD) and transmission electron microscopy. Full width at half maximum XRD values improved from 672 to 378 arcsec by growth on SOI instead of Si substrates. The GaN layers grown directly on Si substrates are highly resistive while all as-grown GaN layers on SOI substrates are unintentionally n type. For a 1–2 μm thick GaN layer grown on SOI, the ele...

Impact of doping and MOCVD conditions on minority carrier lifetime of zinc- and carbon-doped InGaAs and its applications to zinc- and carbon-doped InP/InGaAs heterostructure bipolar transistors

The impact of doping and metalorganic chemical vapour deposition growth conditions on the minority carrier lifetime of zinc- and carbon-doped InGaAs is reported. Room temperature photoluminescence measurements have been employed to obtain direct information on the non-radiative lifetime of the materials. Low growth temperature and low V/III ratio lead to the lower carrier lifetime of the carbon-doped InGaAs samples. InP/InGaAs heterostructure bipolar transistors were grown and fabricated using both zinc- and carbon-doped InGaAs layers as the base regions. The current gain values measured for these devices agree well with the values calculated from the carrier lifetime and mobility/diffusion coefficient measurements.

Minority carrier lifetime in MOCVD-grown C- and Zn-doped InGaAs

Heavily C-doped p-type InGaAs has been successfully grown by metalorganic chemical vapor deposition using CBr/sub 4/ as a C precursor. A doping concentration as high as 2/spl times/10/sup 19/ cm/sup -3/ has been reached for as-grown (non-annealed) samples. Photoluminescence measurements have been employed to obtain and compare the non-radiative lifetimes in C- and Zn-doped InGaAs. The minority carrier lifetime of as-grown InGaAs:C samples is significantly lower than for as-grown InGaAs:Zn for the same doping concentration. Carrier lifetimes range from 373 ps (p=6.6/spl times/10/sup 16/ cm/sup -3/) to 1.5 ps (p=2.3/spl times/10/sup 19/ cm/sup -3/) in as-grown InGaAs:C, and from 6.8 ns (p=5.0/spl times/10/sup 16/ cm/sup -3/) to 16.8 ps (p=2.1/spl times/10/sup 19/ cm/sup -3/) in InGaAs:Zn, respectively. InGaAs:Zn grown at the same low temperature (450/spl deg/C) as InGaAs:C has a higher minority carrier lifetime. The minority carrier lifetime difference between InGaAs:Zn and InGaAs:C samples is attributed to lower V/III ratio and hydrogen passivation, as well as, lower growth temperatures for the carbon doped InGaAs samples.

Nonlinear optical response of GaN layers on sapphire: The impact of fundamental beam interference

GaN layers grown by metalorganic chemical-vapor deposition were characterized by optical second- and third-harmonic generation techniques. The angular dependence of the second-harmonic intensity in transmission showed a c-textured growth of the GaN layers on the sapphire substrates. The measured ratios d33/d15 and d33/d31 are equal to −2.02 and −2.03, respectively, which is indicative of a wurzite structure of the GaN layers. The measured d33 is 33 times that of the d11 of quartz. Fine oscillations were observed in the measured second- and third-harmonic angular dependencies that are explained by taking into account the interference of the fundamental beam in the GaN/sapphire structure.

Comparison of DC and high-frequency performance of zinc-doped and carbon-doped InP/InGaAs HBTs grown by metalorganic chemical vapor deposition

Zinc and carbon-doped InP/InGaAs heterojunction bipolar transistors (HBTs) with the same design were grown by metalorganic chemical vapor deposition (MOCVD). DC current gain values of 36 and 16 were measured for zinc and carbon-doped HBTs, respectively, and carrier lifetimes were measured by time-resolved photoluminescence to explain the difference. Transmission line model (TLM) analysis of carbon-doped base layers showed excellent sheet-resistance (828 /spl Omega///spl square/ for 600 A base), indicating successful growth of highly carbon-doped base (2/spl times/10/sup 19/ cm/sup -3/). The reasons for larger contact resistance of carbon than zinc-doped base despite its low sheet resistance were analyzed. f/sub T/ and f/sub max/ of 72 and 109 GHz were measured for zinc-doped HBTs, while 70-GHz f/sub T/ and 102 GHz f/sub max/ were measured for carbon-doped devices. While the best performance was similar for the two HBTs, the associated biasing current densities were much different between zinc (4.0/spl times/10/sup 4/ A/cm/sup 2/) and carbon-doped HBTs (2.0/spl times/10/sup 5/ A/cm/sup 2/). The bias-dependant high-frequency performance of the HBTs was measured and analyzed to explain the discrepancy.

Impact of GaN buffer growth conditions on photoluminescence and X-ray diffraction characteristics of MOVPE grown bulk GaN

Properties of metalorganic vapor phase epitaxy (MOVPE) grown GaN bulk layers with varying GaN buffer growth conditions are characterized by low-temperature (6K) photoluminescence (LT-PL) and X-ray diffraction (XRD). Full width at half-maximum (FWHM) of the near-bandedge emission of undoped layers is between 4.9 and 10 meV, exhibiting no distinct dependence on buffer growth conditions. PL as well as photoreflectance measurements allowed the identification of neutral-donor bound exciton (D/sub 0/X) emission at /spl sim/3.48 eV, and free A and B exciton emission lines at /spl sim/6 and /spl sim/15 meV higher energies, respectively. UV/yellow luminescence integrated intensity ratio and XRD FWHM show clear dependence on buffer growth conditions. Decreasing buffer thickness results in increasing PL intensity ratio and decreasing XRD FWHM. For thicker buffers, increasing the temperature ramping time between buffer and bulk growth also improves optical layer quality. Si-doped GaN was grown with carrier concentrations between 9/spl times/10/sup 17/ cm/sup -3/ and 2/spl times/10/sup 19/ cm/sup -3/. The PL peak position decreases with increasing carrier concentration and its FWHM increases due to donor banding effects.

Characterization of carbon induced lattice contraction of highly carbon doped InGaAs

Lattice contraction introduced by the smaller covalent radius of carbon (77 pm) relative to arsenic (120 pm), gallium (126 pm), and indium (144 pm) has been observed in highly carbon doped GaAs. This paper addresses similar effects in heavily doped InGaAs:C layers, which find applications as the base of InP/InGaAs heterojunction bipolar transistors (HBTs). Heavily carbon doped InGaAs epilayers (p>1/spl times/10/sup 19/ cm/sup -3/) have been grown by metalorganic chemical vapor deposition (MOCVD) using CBr/sub 4/ as the carbon precursor. The lattice contraction effect induced by carbon incorporation has been studied in such samples by extending the technique previously reported for heavily doped GaAs:C. High-resolution double crystal X-ray diffraction (DXRD) as well as Hall measurements have been performed for this purpose. The experiments clarify the way lattice contraction takes place in case of strong carbon incorporation in InGaAs:C samples. They also show that InGaAs:C becomes increasingly compensated as the doping concentration increases. The study has direct impact on the development of high quality InP-based HBTs.

Photoluminescence Characteristics of GaN Layers Grown on Soi Substrates and Relation to Material Properties

GaN layers were grown by MOCVD on Silicon on Insulator (SOI) substrates in an effort to improve the material quality compared to more traditionally employed sapphire substrates. Their photoluminescence properties are reported and found to exhibit an intense and relatively large PL band around 3.47eV at low temperature (7K). This is about 10meV lower than the PL energy of samples grown on sapphire substrates and suggests the presence of lower strain in the layers which is expected for compliant growth on SOI substrates. The shape of the main PL peak appears to indicate that Silicon diffusion takes place from the substrate during growth. The behavior of the PL spectra is studied as a function of temperature. The GaN films show good overall electrical properties with Hall mobilities at room temperature in the range of 150 to 300cm 2 /Vs and background carrier concentration from 2.9 to 3.9×10 19 cm −3 .The promising optical and electronic features of these layers could be of great interest for the development of high quality optical and electronic devices.