H. Hendriks

Carbon doping and lattice contraction of GaAs films grown by conventional molecular beam epitaxy

Carbon‐doped GaAs films have been grown by solid‐source molecular beam epitaxy using a graphite filament. The films were doped from 1×1015 cm−3 to 5×1019 cm−3 and the resulting mobilities are equivalent to beryllium‐doped films. A slight dependence of As4/Ga flux ratio on carbon doping was observed. The use of either As2 or As4 did not significantly affect the carbon doping concentrations. Lattice contractions were observed for films doped heavily with carbon or beryllium. For a given doping concentration the contraction is more significant for carbon doping which is consistent with the smaller tetrahedral covalent radius of carbon compared to beryllium. Good agreement between observed and calculated lattice contractions with carbon doping is obtained. Annealing studies on a film doped with carbon at 5×1019 cm−3 indicate that the electrical properties and lattice contraction are quite stable.

Carbon doping of MBE GaAs and Ga0.7Al0.3As films using a graphite filament

Carbon doped GaAs and Ga0.7Al0.3As films have been grown by molecular beam epitaxy using a resistively heated graphite filament. At moderate doping levels, the effect on carbon doping of the VIII flux ratio and the nature of the arsenic species was found to be minor. The GaAs films were doped from 1X1015 to 5X1019 cm-3 and the resulting hole mobilities were equivalent to beryllium doped films. Excellent doping uniformity was obtained for 3-inch diameter films. Ga0.7Al0.3As films were also doped from 9X1017 to 3.4X1019 cm−3. For the highest carbon doped films, lattice contractions were observed which were greater than for beryllium doping. The lattice contractions were analyzed with a model using tetrahedral covalent radii.

Photoreflectance characterization of AlGaAs/GaAs modulation‐doped heterostructures

Photoreflectance (PR) and reflectance have been applied to characterize undoped and modulation‐doped heterostructures of AlGaAs/GaAs grown by metal‐organic chemical vapor deposition. The PR spectra were taken on these samples after sequential etching steps in a phosphoric acid etch to study the effects of the surface electric field, the heterointerface, and the two‐dimensional electron gas. PR spectra were also taken with an external electric field applied through a transparent gate electrode. The results show that the oscillations appearing near the bandgap energy of GaAs are Franz–Keldysh oscillations originating from the large surface electric field. The surface electric field of the heterostructures can be modified through the application of an external electric field or by etching. The oscillation period is observed to increase with increasing reverse bias or with etching of the GaAs cap layer and the PR features disappear at a forward bias of 0.45 V. The very sharp features associated with the GaAs ...

Photoluminescence characterization of pseudomorphic modulation‐doped quantum wells at high carrier sheet densities

A systematic study has been made of the photoluminescence spectra of modulation‐doped strained‐layer quantum wells at high electron sheet densities. Peaks associated with both the n=1 and n=2 electron subbands are observed, and the relative intensities are shown to be a result of the symmetry properties of the quantum wells. It is demonstrated that only the full width half maximum of the n=2 subband peak is useful for characterizing high carrier densities.

Carbon tetrabromide carbon doping of molecular beam epitaxial (GaAs) films

GaAs films were doped with carbon up to a hole concentration of 1.3×1020 cm−3 using CBr4 vapor. The material quality of the heavily doped films was found to be better than that obtained using evaporated carbon. Improvements at the highest doping levels include better surface morphology, higher hole mobilities, significantly stronger photoluminescence, and near unity substitutional incorporation. Doping pulses created using CBr4 exhibited abrupt transitions. From the results it is suggested that the material quality of the films doped with evaporated carbon are degraded at high doping levels due to surface combination of reactive carbon species.

Improved pseudomorphic high electron mobility transistor structures on InGaAs substrates

Single and double pulse doped pseudomorphic high electron mobility transistor structures with 110-A-thick InGaAs channel layers have been grown on InxGa1−xAs substrates (x=0.04; 0.065) and GaAs substrates. For In0.23Ga0.77As channel layers, higher electron mobilities were obtained on In0.04Ga0.96As substrates due to reduced strain. Transmission electron microscopy micrographs on a GaAs-based sample exhibited a roughened selectively doped heterojunction but no detected misfit dislocations. Pseudomorphic structures with In0.27Ga0.73As channel layers were also grown on In0.065Ga0.935As substrates with good transport and optical properties. The properties of the analogous structure grown on GaAs were severely degraded. Transmission electron microscopy micrographs on the GaAs sample showed a very rough selectively doped heterojunction with misfit dislocations.

InAlAs/InGaAs high electron mobility transistors on low temperature InAlAs buffer layers by metalorganic chemical vapor deposition

InAlAs/InGaAs high electron mobility transistors (HEMT) with excellent high frequency performance were demonstrated. Device sizes of 0.25×50 μm and 0.10×50 μm showed current gain cutoff frequencies of 143 and 205 GHz, respectively. The HEMT structures were grown on a low temperature InAlAs buffer layers designed to eliminate conductive impurity spikes situated at the epitaxial/substrate interface. The highly resistive buffer layer (2×105 Ω cm) was obtained at a growth temperature of 475 °C using a combination of trimethylarsenic and arsine as the arsenic sources.

Observation of boron‐related photoluminescence in GaAs layers grown by molecular beam epitaxy

Boron‐doped GaAs films grown by molecular beam epitaxy have been studied by photoluminescence. Two boron‐related peaks have been observed in the spectra. The temperature dependence of these peaks is characteristic of acceptor levels, and a quantitative analysis yields activation energies of 71–72 and 188 meV. While the peak with the lower activation energy can be assigned with some confidence to the BAs0/− level, the second peak may be due to a BAs‐SiGa complex rather than the BAs−/−− level.

Si delta‐doped field‐effect transistors by atmospheric pressure metalorganic chemical vapor deposition

Si delta‐doped GaAs field‐effect transistors (FETs) are demonstrated by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) and characterized by Hall‐effect, capacitance‐voltage (C‐V), and Shubnikov de‐Haas measurements. The Si delta doping was accomplished by interrupting the growth and flowing silane with controlled timing under an arsenic overpressure. Devices with 0.5 μm gate length (Ns=2.2×1012 cm−2) were fabricated with a maximum extrinsic transconductance of 140 mS/mm and a current gain cutoff frequency of 17 GHz. The transconductance as a function of gate voltage showed a plateau region through a range of 1.5 V further supporting spatial confinement of the electrons.

Low temperature InAlAs buffer layers using trimethylarsenic and arsine by metalorganic chemical vapor deposition

Low temperature (LT) InAlAs buffer layers grown lattice matched to InP substrates using a combination of trimethylarsenic and arsine were demonstrated. The LT InAlAs buffer layer showed excellent surface morphology with a maximum resistivity of 2×105 Ω cm at a growth temperature of 475 °C. Low temperature photoluminescence and Hall‐effect measurements confirming the high quality of epitaxial layers grown on top of the LT InAlAs buffer layer. Electrochemical capacitance voltage measurements consistently confirmed the absence of conductive impurity spikes at the epitaxial/substrate interface.