Search

A study in the growth of GaN x P 1 − x epilayers by chemical beam epitaxy using tertiarybutylphosphine (TBP), ammonia (NH 3 ), and elemental Ga or triethylgallium is reported. Monitoring reflection high-energy electron diffraction (RHEED) intensity oscillations, we observe that both group-III- and group-V-induced incorporation rates are increased when NH 3 is introduced into a single cracker with TBP. From the difference in the periods of group-V-induced RHEED intensity oscillations, a 16% N incorporation is expected, but X-ray rocking curve measurement shows only 0.08% N. Using separate TBP and NH 3 crackers results in no enhancement in incorporation rates. We conclude that the cracking efficiency of TBP is increased with NH 3 co-injection.

In this paper we evaluate the use of tris-dimethylaminoarsenic (TDMAAs), tris-dimethylaminophosphorus (TDMAP), and tertiarybutylphosphine (TBP) as safer alternative sources in CBE. TDMAAs is a viable alternative to arsine for growing GaAs. When In-containing compounds were grown using uncracked TDMAAs or TDMAP with trimethylindium, indiumenhanced TDMAP or TDMAAs desorption was observed, resulting in In droplets on the surface. InP can be grown only if TDMAP is cracked, but many surface defects are observed and the growth rate is very sensitive to the growth temperature. When TBP is used, however, a specular surface can be achieved, and the InP growth rate is independent of substrate temperature from 440 to 480°C. TDMAAs and TDMAP are found to etch GaAs, InP, and GaP, which shows potential applications in in-situ etching and regrowth.

Tris-dimethylaminoarsenic (TDMAAs) is shown to be a viable alternative to arsine. With Ar ion laser irradiation, the growth enhancement at low substrate temperatures, compared to using arsine or arsenic, has a wider temperature range by ∼100°C, indicating a photochemical effect in addition to the photothermal effect. Furthermore, TDMAAs can be used to etch GaAs at a higher temperature by amine radicals as cracked TDMAAs has no etching effect. The etch rate can be enhanced by Ar ion laser irradiation through local heating. Smooth surface morphology in selective-area growth can be obtained with cracked TDMAAs. Diiodomethane is also shown to be a viable carbon-doping source, and laser-enhanced doping has a photochemical component as well. With cracked TDMAAs, a high 10 19 cm -3 hole concentration can be obtained.

The growth of InxGaj1−xAs (x = 0.13–0.25) on GaAs by chemical beam epitaxy (CBE) and laser-modified CBE using trimethylindium (TMIn), triethylgallium (TEGa), and tris-dimethylaminoarsenic (TDMAAs) has been studied. Reflection high-energy electron diffraction measurements were used to investigate the growth behavior of InGaAs at different conditions. X-ray rocking curve and lowtemperature photoluminescence (PL) measurements were used to characterize the InGaAs/GaAs pseudomorphic strained quantum well structures. Good InGaAs/GaAs interface and optical property were obtained by optimizing the growth condition. As determined by the x-ray simulation, laser irradiation during the InGaAs quantum well growth was found to enhance the InGaAs growth rate and reduce the indium composition in the substrate temperature range studied, 440–500°C, where good interfaces can be achieved. These changes, which are believed to be caused by laser-enhanced decomposition of TEGa and laser-enhanced desorption of TDMAAs, were found to depend on the laser power density as well. With laser irradiation, lateral variation of PL exciton peaks was observed, and the PL peaks became narrower.

Highly p-type carbon-doped GaAs epitaxial layers were obtained using diiodomethane (CI2H2) as a carbon source. In the low 1019 cm−3 range, almost all carbon atoms are electrically activated and at 9 × 1019 cm−3, 91% are activated. The carbon incorporation efficiency in GaAs layers grown by metalorganic molecular beam epitaxy (MBE) and chemical beam epitaxy (CBE) is lower than that by MBE due to the site-blocking effect of the triethylgallium molecules. In addition, in CBE of GaAs using tris-dimethylaminoarsenic (TDMAAs), the carbon incorporation is further reduced, but it can be increased by cracking TDMAAs. Annealing studies indicate no hydrogenation effect.

We shall first describe some unique features of metal-organic molecular beam epitaxy (MOMBE), then focus on the use of safer alternative precursors to arsine, and finally report on the effect of argon ion laser irradiation on the MOMBE of GaAs and GaAs InGaAs quantum well structures.

Selective-area epitaxy of carbon-doped (Al)GaAs by chemical beam epitaxy (CBE) on (100) GaAs substrates patterned with SiO 2 has been studied. Triethylgallium, trimethylaluminum, tris-dimethylaminoarsenic (TDMAAs) and diiodomethane were used as precursors. True selectivity of GaAs and AlGaAs with a growth rate of 0.5 μm/h is achieved at a growth temperature as low as 470 o C. A flat GaAs regrown surface can be obtained, however, only by thermally cracking the TDMAAs source at 350 o C. The growth rate of GaAs:C layers is independent of the stripe openings down to about 5 μm. A growth rate enhancement is observed when the feature size is less than 5 μm. The «rabbit ear» thickness can be significantly reduced if the stripe opening is less than 5 μm or if the V/III incorporation ratio is low. A heterojunction bipolar transistor (HBT) with selectively regrown GaAs/AlGaAs:C eternal base layers has been successfully fabricated. It exhibits at least a 60% improvement in the base sheet resistance compared to the original HBT structure, demonstrating the potential of selective-area growth by CBE

The growth of GaAs by chemical beam epitaxy using triethylgallium and trisdimethylaminoarsenic has been studied. Reflection high-energy electron diffraction (RHEED) measurements were used to investigate the growth behavior of GaAs over a wide temperature range of 300–550°C. Both group III- and group Vinduced RHEED intensity oscillations were observed, and actual V/III incorporation ratios on the substrate surface were established. Thick GaAs epitaxial layers (2–3 μm) were grown at different substrate temperatures and V/III ratios, and were characterized by the standard van der Pauw-Hall effect measurement and secondary ion mass spectroscopy analysis. The samples grown at substrate temperatures above 490°C showed n-type conduction, while those grown at substrate temperatures below 480°C showed p-type conduction. At a substrate temperature between 490 and 510°C and a V/III ratio of about 1.6, the unintentional doping concentration is n ∼2 × 1015 cm−3 with an electron mobility of 5700 cm2/V·s at 300K and 40000 cm2/V·s at 77K.

The growth behavior of Ar-ion-laser-assisted metalorganic molecular beam epitaxy (MOMBE) of (001) GaAs, in the temperature range 330–450°C with triethylgallium (TEGa) and As 4 , was studied by monitoring the specular-beam intensity oscillations of reflection high-energy electron diffraction (RHEED), with the laser turned on and off. The decomposition rate of TEGa is enhanced under Ar + laser irradiation. The Ar + laser also enhances the surface migration of adsorbates and arsenic desorption. In the arsenic-controlled growth regime, the growth rate increases monotonically at low laser power and tends to saturate at high laser power due to a balance between enhanced decomposition of TEGa and desorption of arsenic.

A model of service quality is presented which is based on the customer's perspective and a systematic approach to measuring that perspective. Experiences from the telecommunications industry show that this research approach allows for verification of the model and assessment of the validity of the measures. In addition, the results yield actionable data that pinpoint problems and uncover opportunities for improving service. >

A model of telephone service quality from the customer's perspective and a systematic approach to its measurement are discussed. Because the proposed model is designed from the customer perspective and uses a scientific process to assess the quality of the model, it provides an effective way to integrate the voice of the customer into every phase of a business. Examples from the telecommunications industry are used to show the effectiveness of this model in pinpointing service problems and uncovering opportunities for improving service. >

Carbon Nitride (CNX) films have been grown by ion-assisted pulsed-laser deposition (IAPLD). Graphite targets were laser ablated while bombarding the substrate with ions from a broad-beam Kaufman-type ion source. the ion voltage, current density, substrate temperature, and feed gas composition (N2 in ar) have been varied. the resultant films were characterized by Raman, Fourier transform infrared (FTIR), and Rutherford back scattering (RBS) spectroscopy. Samples with -30% N/C ratio have been fabricated. the corresponding Raman and FTIR spectra indicate that nitrogen is incorporated into the samples by insertion into sp2-bonded structures. a low level of C=N triple bonds is also found. as the ion current and voltage are increased with a pure ar ion beam, Raman peaks associated with nanocrystalline graphite appear in the spectr A. adding low levels of nitrogen to the ion beam first reduces the Raman intensity in the vicinity of the graphite disorder peak without adding detectable amounts of nitrogen to the films (as measured by RBS). at higher nitrogen levels in the ion beam, significant amounts of nitrogen are incorporated into the samples, and the magnitude of the “disorder” peak increases. by increasing the temperature of the substrate during deposition, the broad peak due mainly to sp2-bonded C-N in the FTIR spectra is shifted to lower wavenumber. This could be interpreted as evidence of single-bonded C-N; however, it is more likely that the character of the sp2 bonding is changing.

In this paper, we report chemical beam epitaxy (CBE) of GaAs, and for the first time, Arion laser-assisted CBE using triethylgallium (TEGa) and tris-dimethylaminoarsenic (TDMAAs), a safer alternative to arsine. Samples grown at substrate temperatures above 490° C show n-type conduction, while those grown at lower temperatures show p-type conduction. An unintentional doping concentration of n∼lx1016 cm-3 with an electron mobility of 5200 cm2/V.s at 300 K and 16000 cm2/V.s at 77 K have been achieved. These are the best results reported for GaAs grown with TDMAAs. Laser-assisted CBE of GaAs is studied in the substrate temperature range of 240-550°C. There are two different substrate-temperature regions for laser-enhanced growth, 265 to 340°C and 340 to 440°C, which are believed to be caused by different TEGa decomposition mechanisms. The laser-assisted growth with TDMAAs, compared to AS4 or AsH3, shows a wider range of growth enhancement at low substrate temperatures.

We report for the first time laser-modified chemical beam epitaxy (CBE) of InGaAs/GaAs multiple quantum well (MQW) structures using trimethylindium (TMIn), triethylgallium (TEGa), and tris-dimethylaminoarsenic (TDMAAs), a safer alternative to arsine. X-ray rocking curve (XRC) and low-temperature photoluminescence (PL) measurements were used to characterize the pseudomorphic strained quantum well structures. As determined by the X-ray simulation, laser irradiation during the InGaAs well growth was found to enhance the InGaAs growth rate and reduce the indium concentration in the substrate temperature range studied, 440-S00°C, where good interfaces can be achieved. We attribute these changes to laser-enhanced decomposition of TEGa and laser-enhanced desorption of TDMAAs. With laser irradiation, lateral variation of PL exciton peaks was observed, and the PL peaks became narrower.

Metalorganic molecular beam epitaxy (MOMBE) of GaAs using triethylgallium (TEGa) and As4 has been studied by reflection high-energy electron diffraction (RHEED). The effect of varying the group-Ill flow rates and group-V beam flux on the growth rate has been investigated over a wide range of substrate temperatures. For a given arsenic flux, the GaAs growth rate first increases linearly as the TEGa flow rate increases. This linear relation extends up to a certain TEGa flow rate, where the growth rate reaches its maximum value. When the TEGa flow rate is increased above this critical value, the growth rate decreases and reaches a stabilized value. From a study of both group-Ill and group-V induced RHEED intensity oscillations, we find that the V/Ill incorporation ratio is unity at the transition point. Compared to conventional molecular beam epitaxy (MBE), MOMBE behaves differently when the V/Ill incorporation ratio is less than unity. The transition region between V/III>I and V/III

We will present a comparison between GaN grown on c - and r -plane sapphire by gas-source molecular beam epitaxy (GSMBE) using solid source elemental Ga with uncracked ammonia (NH 3 ). Improved GaN film quality was found for samples grown at substrate temperatures above 700°C with optimized temperatures at 780°C. GaN deposited on a low-temperature (∼ 350°C) GaN buffer layer grown using an rf-plasma radical beam source exhibited poor photoluminescence (PL) intensity and carrier mobility while SEM analysis showed smooth GaN surface morphologies. GaN deposited on an ammonia-grown low-temperature (∼ 550°C) GaN or AlN buffer were found to have improved PL intensity and line widths, GaN surface morphology and carrier mobility. X-ray rocking curve (XRC) data showed that the GaN crystal quality improved as a function of increasing substrate growth temperature independent of buffer layer implementation.