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We examine the epitaxial incorporation behavior of the volatile p-type dopant Mg at high growth temperatures during the molecular beam epitaxy of GaN on the [0001] surface, and report interesting doping behavior. The net Mg incorporation is independent of the arriving Mg flux over a flux variation of two decades, and dependent strongly on the growth temperature of the epilayer, limiting the net hole concentrations obtainable to the low 1017 cm−3 range. These results are explained in terms of incorporation either through a surface Mg phase, or via the availability of specific sites on the surface for Mg incorporation.

We present experimental evidence that minority electron transport across a thin, quasineutral p+ GaAs region is limited by the thermal velocity of the electrons rather than by conventional diffusive transport. A set of GaAs homojunction np+n transistors with base widths of 4000, 2000, 1000, and 500 A was fabricated and characterized. The diffusive model predicts that the dc collector current of the 500‐A base width transistors should be eight times larger than the collector current of transistors with a 4000‐A‐wide base. The experimental results, however, show only a factor of ∼3.5 increase in collector current. The measured collector current versus base width characteristic agrees well with theoretical treatments of thin‐base transport. These new results present evidence of quasiballistic electron transport in p+ GaAs and have important implications for GaAs transistor design.

Ge segregation at SiGe/Si heterointerfaces has been studied for films deposited by atmospheric pressure chemical vapor deposition (APCVD), ultrahigh vacuum CVD (UHV/CVD) and molecular beam epitaxy (MBE). Profiles were taken by secondary‐ion‐mass‐spectroscopy (SIMS) of samples grown with these techniques at the same growth temperatures and Ge concentrations. The MBE grown profiles are dominated by segregation of Ge into the Si top layer in the temperature range from 450 to 800 °C. SiGe/Si interfaces deposited by UHV/CVD at elevated temperatures are smeared, but at 515 °C and below the interfaces are abrupt within the resolution of the SIMS. Heterostructures grown by APCVD show abrupt interfaces and no indication of Ge segregation in the investigated temperature range from 600 to 800 °C. Surface passivation by hydrogen appears to be responsible for the suppression of the Ge segregation in CVD processes.

When a high dose of As is implanted (e.g., 25 keV, 3×1015 cm−2) into B‐doped Si and the sample is subsequently annealed at 900 °C/5 min, pronounced segregation of the B into the implanted region occurs. This creates a B‐depleted region beyond the As profile. It is demonstrated that the B segregation is driven primarily by the implantation induced damage rather than by As‐B chemical and/or by electric field effects. The B segregation is nearly complete after a relatively low temperature (≲600 °C/30 min) anneal. Two‐dimensional device simulations show that the B depletion observed here can account for ≂50 mV threshold voltage roll off (at a drain bias of 0.1 V) in a Si metal–oxide–semiconductor field effect transistor of 0.2 μm gate length.

The thermal stability of epitaxial silicon‐carbon alloys grown by molecular beam epitaxy on (001) silicon was investigated using high resolution x‐ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy measurements. Different superlattices, with alloy compositions of Si0.997C0.003, Si0.992C0.008, and Si0.985C0.015, all nominally 6 nm thick, with 24 nm Si spacer layers were employed. Annealing studies determined that there are different pathways to strain relaxation in this material system. At annealing temperatures of 900 °C and below, the structures relax only by interdiffusion, indicating that these layers are stable during typical device processing steps. At temperatures of 1000 °C and above, SiC precipitation dominates with enhanced precipitation in the Si1−xCx layers with the highest initial carbon content.

Rapid interdiffusion occurs at thin‐film SiGe/GaAs interfaces when samples are annealed in oxygen containing ambients. Secondary ion mass spectroscopy and AlAs/GaAs superlattice disordering indicate that Ge and/or Si diffuse to depths of 200 nm after oxidation at 800 °C for 30 min. Negligible diffusion is detected for anneals in forming gas. Dissociation, out‐diffusion, and oxidation of the GaAs substrate at the surface are associated with the phenomenon.

It was recently inferred from low‐temperature transport measurements that DX centers are not formed in Sn‐doped AlGaAs grown by metalorganic vapor phase epitaxy at T≥850 °C. Deep level transient spectroscopy measurements reported here show that DX centers are present in this material. The high conductivity measured at low temperature comes from parallel conduction in the underlying GaAs due to Sn diffusion during growth at high temperature.

We have synthesized pseudomorphic Si1−yCy (y≤0.05) alloys and strained layer superlattices on silicon by molecular beam epitaxy using solid sources for carbon and silicon. The introduction of C into substitutional sites in the silicon lattice is kinetically stabilized by low‐temperature growth conditions (500–600 °C) and relatively high Si fluxes, against extremely low C solubility (10−6 at 1420 °C) and the thermodynamically favored silicon carbide phases. Higher temperature growth leads to an islanded morphology. At lower temperatures, disruption of epitaxy occurs via the formation of highly twinned layers or even amorphous growth. The temperature window for alloy growth is reduced as the C concentration is increased. X‐ray diffraction, transmission electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy confirm the growth of pseudomorphic, tetragonally strained alloy layers with no detectable silicon carbide precipitation. These alloy layers allow for the engineering of Si‐based lat...

Double‐heterostructure light‐emitting diodes (LEDs) consisting of an n‐Ga0.51In0.49P emitter, a carbon‐doped p‐GaAs active layer, and a p‐Al0.30Ga0.70As cladding layer have been grown by gas source molecular beam epitaxy with halomethane carbon doping sources. CCl4 and CHCl3 have been used to vary the active layer C doping level from 1018 to 1020 cm−3. Measurements of LED optical modulation bandwidth indicate that the bandwidth increases with C doping, attaining a record value of 1.6 GHz at 1020 cm−3 C concentration. The LED radiance is observed to decline significantly in the 1019–1020 cm−3 range.

Single‐heterostructure light‐emitting diodes (LEDs) consisting of a wide band‐gap N‐Ga0.51In0.49P emitter and a heavily carbon‐doped p‐GaAs active layer have been grown by metalorganic molecular beam epitaxy. Trimethygallium has been utilized to dope the GaAs active layer for a hole concentration of 1.5×1020 cm−3 in order to reduce the radiative lifetime of minority carriers in GaAs. The cw electroluminescent spectra of these LEDs indicate that the injection efficiency of the Ga0.51In0.49P/GaAs heterojunction is not degraded by carbon redistribution, even in the absence of an undoped spacer layer between the GaAs active layer and the Ga0.51In0.49P emitter layer. The transient optical response of the LEDs determines an optical 3 dB bandwidth in the range of 0.6–2.0 GHz. The external brightness of the carbon‐doped LEDs is shown to be approximately a factor of 20 lower than that of double‐heterostructure LEDs containing active layers more moderately doped with Be at 2×1018 cm−3.

Intentional oxygen doping (≳1017 cm−3) of GaAs and Al0.30Ga0.70As epitaxial layers was achieved during metalorganic vapor phase epitaxy through use of an oxygen‐bearing metalorganic precursor, dimethylaluminum methoxide (CH3)2AlOCH3. The incorporation of oxygen and very low levels of Al (AlAs mole fraction

Carrier concentrations at a level of ≳1×1019 cm−3 were achieved when Si‐capped GaAs underwent rapid thermal oxidation (RTO) in Ar+0.1% O2 ambient at 850–1000 °C for 10–60 s followed by rapid thermal annealing (RTA) in Ar ambient at 850–950 °C. Carrier concentrations in the RTO only samples were in the range of 2–5×1018 cm−3. Kinetic data on the diffusion of Si under RTO and RTO+RTA conditions are presented. The enhancement in the electrical activation of the diffused Si during RTA appears to be partly due to its local atomic rearrangement and partly due to redistribution in the GaAs. Ohmic contacts to the doped layer were made using Au‐Ge‐Ni alloy and contact resistances of ≲0.1 Ω mm were obtained.

Carbon tetrabromide (CBr4) and bromoform (CHBr3) have been studied as carbon doping sources for GaAs grown by gas source molecular beam epitaxy (GSMBE) with elemental Ga and thermally cracked AsH3. Hole concentrations in excess of 1×1020 cm−3 have been measured by Hall effect in both CBr4‐ and CHBr3‐doped GaAs, which agrees closely with the atomic C concentration from secondary‐ion mass spectrometry, indicating complete electrical activity of the incorporated carbon. The GaAs growth rate is unaffected by the CBr4 and CHBr3 fluxes over the range of dopant flow investigated. The efficiencies of carbon incorporation from CBr4 and CHBr3 are, respectively, 750 and 25 times that of trimethylgallium (TMG), which is commonly employed as a carbon doping source in metalorganic MBE (MOMBE). The sensitivity of carbon incorporation to varying substrate temperature and V/III ratio has been observed to be significantly reduced with CBr4 and CHBr3 from that obtained under similar growth conditions with TMG in MOMBE.

Strong n but weak p‐carrier passivation was observed when Si‐ and Mg‐implanted/annealed GaAs samples were exposed to a 2D plasma under identical conditions. Even though a discrete band of dislocation loops was present in both the samples, the 2D distribution in the two cases was remarkably different. In the Si‐implanted sample the 2D followed the carrier distribution, whereas in the Mg‐implanted sample it followed the distribution of dislocation loops. Phenomenological mechanisms of 2D interaction with dopants/dislocations in GaAs are postulated.

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It is demonstrated using rapid thermal annealing that the electrical activation of Si+‐implanted GaAs capped with a plasma‐enhanced chemical vapor deposited (PECVD) silicon nitride (SixNy) layer requires longer annealing times compared to capless annealing. The SIMS profiles of 2H from the GaAs samples onto which SixNy caps were deposited using deuterated ammonia showed that deuterium atoms diffuse readily into the implanted region during PECVD. The improvement in the electrical activation of the capped samples with annealing time correlates directly with decreasing concentration of the 2H in the GaAs. It is postulated that the H atoms diffusing into GaAs during PECVD are trapped by the implantation‐induced damage and the delay in electrical activation corresponds to the time required for the release of the trapped H.

F+ co‐implantation at different doses and energies was performed into GaAs already implanted with Be+ at high dose (1015 cm−2) and low energy (20 keV), in order to reduce the beryllium diffusion during post‐implant annealing. The redistribution behavior of Be and associated electrical effects were studied by secondary‐ion mass spectrometry, transmission electron microscopy (TEM), Hall effect measurements, and current‐voltage profiling. Be outdiffusion was reduced by co‐implantation of F; more than 80% of the implanted Be was retained during rapid thermal annealing up to 850 °C. The dose and energy of the F implant strongly influenced Be electrical activation efficiency. High activation, up to 48.5%, was obtained when F was co‐implanted at high dose (1015 cm−2) and low energy (10 keV). Hole profiles shown reduced electrical activation in the region where F and Be profiles overlapped and TEM studies indicated the formation of {111} coherent plates, possibly BeF2 precipitates, in the same region. The reducti...

The quantitative analysis of carbon levels in thin layers of semiconductor materials is usually limited by poor detection limits. While several qualitative techniques for detecting carbon exist, secondary ion mass spectroscopy (SIMS) has been the primary tool for obtaining depth profiles of carbon in thin films. The presence of carbon compounds in the residual gas background of the SIMS instrument typically limits the carbon detection limits to ∼1017 cm−3 under standard operating conditions. If the carbon contamination in material processing could be studied with 13C labeled compounds, detection sensitivities should be far better. We have shown here that with this approach and the judicial choice of the analyte ion As13C− the detection sensitivity can be lowered by more than two orders of magnitude. We have applied this technique to the study of the incorporation of carbon from isotopically enriched CH4, C2H2, and C2H4 during the epitaxial growth of GaAs by the metalorganic vapor phase epitaxy technique. ...

The controlled incorporation of carbon has been demonstrated for the metalorganic vapor phase epitaxy of GaAs. Carbon levels between 1016 and 1019 cm−3 can be achieved under typical growth conditions by using Ga(CH3)3 and either As(CH3)3 or mixtures of As(CH3)3 and AsH3. The carbon incorporation into GaAs goes through a minimum with growth temperature at ∼650 °C when using Ga(CH3)3 and As(CH3)3. The controlled addition of AsH3 monotonically decreases the carbon incorporation. The high carbon levels (≳1–2×1019 cm−3), greater than the reported solid solubility, are thermally stable with a low diffusion coefficient. The GaAs:C layers exhibit a low deep level concentration, ∼1013 cm−3, with only a single midgap trap present.