Diethylgallium chloride Et2GaCl
Vapor pressure of diethylgallium chloride Et2GaCl was measured by capacitance manometer at temperatures 5?°C to 60°C. [351]
Et2GaCl is dominantly associated as multimers in the gas phase.[mentioned in 435]
Adsorption dynamics of diethylgallium chloride on the GaAs(100) As-rich c(2 × 8) surfaces was studied. Residence times and sticking coefficients were monitored using time-resolved molecular beam/surface scattering, the adsorption of these molecules was precursor mediated. The accommodation of the kinetic energies of the molecules on the surfaces resulted in the trapping of the molecules; most of the trapped molecules were chemisorbed at room temperature and trapping-desorption was insignificant until the surface coverage was close to saturation.[432]
Et2GaCl for GaAs MOCVD / MOVPE
Diethylgallium chloride Et2GaCl and AsH3 have been applied for the selective epitaxy of GaAs by MOVPE. No GaAs deposition happens on SiO2, Si3N4, or SiONx under normal growth conditions (600–800°C, 0.1 atm reactor pressure). Unlike other forms of selective epitaxy, there was no enhanced growth rate at the edge of the selectively grown regions. The selectivity was a result of the reduced adsorption of the growth precursor, probably GaCl, on the masking material relative to the exposed GaAs areas. Very good electrical properties of the interface between the selectively grown material and the underlying substrate with no interfacial potential barrier were achieved by appropriate pre-growth treatment [434]
Diethylgallium chloride Et2GaCl (DEGaCl) with AsH3 as group V-source, and H2 as carrier gas, has been applied as precursor for the MOVPE growth of GaAs in a hot-wall system at growth temperature 350-700°C and reactor pressures 0.10–10 Torr (the substrates were mounted parallel to the average gas flow direction). The very low temperature at which the growth rate is reaction-limited was explained in terms of preferential conversion of DEGaCl to a species that is more readily incorporated as GaAs, such as GaCl. Monotonic decrease of the growth rate at higher temperatures with downstream location and drastic drop in growth rate at even higher temperatures, probably result from the depletion of GaCl in the reactor, and/or a lower supersaturation of GaCl in the gas phase due to increasing concentrations of HCl downstream the reactor. The carrier concentration were below 2.5·1014 cm-3 at 450°C and increases at higher temperatures to 5·1015 cm-3 n-type at 650°C. [435]
Diethylgallium chloride Et2GaCl has been used as precursor for growth of GaAs by MOCVD at low growth temperatures (400–800°C) and low reactor pressures (10–78 Torr) have been investigated. GaAs growth rate is essentially independent of temperature at high reactor pressures and temperatures. The growth efficiency was reduced compared to GaMe3 precursor in the same reactor. Carbon and silicon were the major impurities in the epitaxial GaAs; carbon concentration increased with decreasing growth temperature. Silicon depth profiles, obtained from low growth temperature samples, indicate surface segregation of Si during the growth (Si concentration increased towards the sample surface reaching a plateau, after which uniform doping was observed; the magnitude of the Si concentration within this plateau region increased with decreasing growth temperature) Si in these samples was either electrically inactive or highly compensated by the carbon acceptors. (according to electrical measurements). [436]
Diethyl gallium chloride Et2GaCl (DEGaCl) with ammonia as nitrogen source have been applied as precursor for MOVPE) of GaN on basal plane sapphire resulting in hydride vapor-phase epitaxy (HVPE)-like growth chemistry. Growth rate and efficiency of the Et2GaCl-based growth decreased with increasing temperature when compared to GaMe3-based growth under similar conditions. The standard ‘two-step’ GaN growth process (low temperature buffer followed by high temperature GaN layer) was performed using the Et2GaCl-NH3 precursor combination and compared to GaMe3 / NH3 process. under identical reactor conditions. According to authors, Et2GaCl-based growth revealed an improved growth behavior under identical growth conditions to the conventional GaMe3/NH3 growth. The improved growth behavior was attributed to the ‘nearer-to-equilibrium’ growth front that could result from the presence of HCl-related etching reactions. XRD, Hall, AFM, C-V, PL measurements were carried out to provide a direct comparison of materials properties associated with these growth precursors. [437]
Diethyl gallium chloride Et2GaCl was studied as an alternative gallium source for the MOVPE and HVPE lateral epitaxial overgrowth (LEO) of GaN on SiO2-masked (0001) GaN substrates. High-quality coalesced and planar ELO GaN has been fabricated by both growth chemistries. The decomposition of Et2GaCl to GaCl during MOVPE produced growth conditions similar to hydride VPE near the growth front producing increased lateral growth rates; controlled vertical and sloped facets were produced through the choice of the reactor operating conditions. LEO tilting angles decrease with decreasing lateral-to-vertical growth rate ratio according to XRD. LEO GaN using Et2GaCl source has smaller kink density along the growing facets under the conditions required for rapid and smooth coalescence. The increased lateral growth rates and smoother sidewall facets within Et2GaCl based growth were attributed to the ‘nearer-to-equilibrium’ conditions at the growth front that can result from the presence of HCl-related etching reactions. Growth temperature, V/III ratio, and the in-plane orientation of the mask opening were the main factors influencing lateral and vertical growth rates, overgrowth morphology of LEO GaN structures. High deposition temperature and low V/III ratio increased the lateral growth rate and produce ELO structures with flattened top c-plane of GaN prisms; no void was observable at the coalescence interface.. The use of the Et2GaCl as precursor allows the benefits of HVPE growth to be realized within the MOVPE growth environment. [438]
The regrown GaN interfaces had very high quality with no substantial interface charge (with the appropriate HCl pre‐regrowth surface treatment). SIMS measurements showed no detectable accumulation of impurities at the regrown interface, in contrast to those regrown using the conventional GaMe3‐based chemistry The contact resistivity, as determined by transmission line measurements, was (2–4)×10-7 Ω/cm2 at both 77 and 300 K. [439]
GaEt2Cl for GaAs ALD: Surface chemistry of GaEt2Cl
Surface chemistry of Et2GaCl and GaMe3 on GaAs(100) surface, as related to atomic layer epitaxy (ALE) of GaAs was studied. Diethylgallium chloride was found to deposit GaCl on the GaAs surfaces, with residence time decreasing rapidly with increasing Ga coverage. , according to numerical calculations it can significantly contribute to the self‐limiting Ga deposition during ALE of GaAs. For comparison, GaMe3 surface chemistry was studied: the reaction pathway during Ga deposition is such that at high Ga coverages there is significant GaMe emission (details see under GaMe3 section) [433]
GaEt2Cl for AlGaAs CVD
Et2GaCl in combination with Et2AlCl were successfully employed as precursors for the epitaxial growth of AlxGa1–xAs on GaAs and selective growth of AlxGa1–xAs on GaAs wafers masked with SiO2 or Si3N4. Selectivity of AlxGa1–xAs improved with increasing Et2GaCl mole fraction and with increasing temperature. (Detailed description presented in Et2AlCl section) [353]
GaEt2Cl·AsEt3 for GaAsP CVD
Diethylgalliumchloride-triethylarsine adduct GaEt2Cl·AsEt3, with diethylphoshine Et2PH as P source, was applied as precursor for MOCVD of GaAs1−xPx epitaxial layers (0 < x < 0.6) on GaAs and Ge substrates at 500–650°C. The growth rate strongly depended on the deposition temperature reaching maximum at 600°C. [440]
GanPr2Cl, GanPrCl2 for Ga2O3 CVD
Growth kinetics of Ga2O3 films MOCVD using dipropylgallium chloride nPr2GaCl and propylgallium dichloride nPrGaCl2 was studied; prepared layers were characterized by IR, x-ray spectroscopy and electrical measurements. Thermal decomposition of dipropylgallium chloride was studied by thermal analysis. [352]