Steven K. Brierley

Native donors and acceptors in molecular-beam epitaxial GaAs grown at 200° C

Absorption measurements at 1.1 and 1.2 μm were used along with the known electron and hole photoionization cross sections for EL2 to determine deep donor (EL2‐like) and acceptor concentrations ND=9.9×1019 and NA=7.9×1018 cm−3, respectively, in a 2‐μm‐thick molecular‐beam epitaxial GaAs layer grown at 200 °C on a 2‐in.‐diam semi‐insulating wafer. Both lateral and depth uniformities of ND over the wafer were excellent as was also the case for the conductivity. Band conduction was negligible compared to hopping conduction at 296 K as evidenced by the lack of a measurable Hall coefficient.

Quantitative characterization of modulation‐doped strained quantum wells through line‐shape analysis of room‐temperature photoluminescence spectra

Room‐temperature photoluminescence (PL) has been used to characterize modulation‐doped AlGaAs/InGaAs/superlattice strained layer quantum wells. A phenomenological line‐shape model has been developed which can be fitted to PL spectra in order to obtain key parameters such as the subband energies, Fermi energy, and transition amplitudes. Quantum well sheet densities calculated from fits to the PL spectra (taken at both room temperature and 77 K) have been compared to sheet densities obtained from low‐temperature Hall measurements. It has also been shown how variations in quantum well composition, width, and symmetry can be characterized by shifts in values of the relevant fitting parameters.

Full‐wafer mapping of total and ionized EL2 concentration in semi‐insulating GaAs using infrared absorption

By combining infrared absorption data taken at two different wavelengths in the spectral region in which the native deep donor EL2 absorbs in GaAs, it is possible to determine the distribution of the total EL2 concentration and its filled fraction across a semi‐insulating GaAs substrate. The distributions of net shallow acceptor concentration and free‐electron concentration can then be deduced. Full‐wafer maps of these quantities for a semi‐insulating GaAs wafer are displayed along with Hall effect measurements which confirm the patterns observed optically.

Correlation between the photoreflectance impurity peak in semi‐insulating GaAs and the bulk acceptor concentration

We have measured the strength of the first‐derivative peak observed below the band gap in photoreflectance spectra of semi‐insulating GaAs and found that it is correlated with the bulk residual acceptor concentration. The apparent energy separation of the impurity peak is not fixed, but varies from sample to sample.

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.

Molecular‐beam epitaxial growth of heavily acceptor doped GaAs layers for GaAlAs/GaAs heterojunction bipolar transistors

Heterojunction bipolar transistor (HBT) structures with heavily carbon and beryllium doped base layers were grown in a conventional molecular‐beam epitaxy (MBE) environment. The current gain in the carbon doped structures was reduced by enhanced bulk recombination. For a hole concentration of 5 × 1019 cm−3, the carbon concentration exceeded the hole concentration and is a likely cause of the enhanced recombination. Growth conditions were determined which minimized beryllium diffusion for HBT structures with base layers doped to 1.2 × 1020 cm−3. Lattice contractions were observed at high beryllium doping concentrations. The expected reduction in resistivity with increased beryllium base doping was obtained in the HBT structures. Using HBT structures doped with beryllium at 5 × 1019 cm−3, high‐power performance was obtained at 10 GHz.

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.

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.

Precise determination of indium composition and channel thickness in pseudomorphic high electron mobility transistors using room temperature photoluminescence

Proper composition and thickness of the InGaAs channel in pseudomorphic high electron mobility transistors (PHEMTs) is critical to assuring good device performance. Typically these characteristics have been measured by high-resolution x-ray diffraction. The results presented in this work show that the subband energy levels obtained from line shape analysis of room temperature photoluminescence spectra on these structures can be correlated very well with thickness and composition obtained from x-ray diffraction. Since the photoluminescence measurement and analysis is quite fast, this technique is suitable for rapid, nondestructive screening of PHEMT epitaxial material.

High performance double pulse doped pseudomorphic AlGaAs/InGaAs transistors grown by molecular‐beam epitaxy

Double pulse doped AlGaAs/InGaAs pseudomorphic high electron mobility transistors have been grown by molecular‐beam epitaxy on GaAs substrates. Hall mobilities in excess of 7100 cm2/V s at 300 K and 25 000 cm2/V s at 77 K are obtained with a sheet density of 3×1012 cm−2. Photoluminescence measurements indicate that two electronic subbands are occupied, and the subband energies are determined. The doping pulses are resolved in secondary ion mass spectrometry measurements. Using a double recess process, transistors have been fabricated that have produced state of the art microwave performance. At 10 GHz a 1.2 mm device has simultaneously achieved a power added efficiency of 70%, output power of 0.97 W, and gain of 10 dB.