The first 20Gbit/s 1.3-1.55 mu m wavelength monolithic integrated photoreceiver grown on GaAs substrate has been fabricated using AlGaAs/GaAs HEMTs. At a wavelength of 1.3 mu m, the integrated InGaAs MSM photodiode has a responsivity of 0.32A/W and the photoreceiver has a -3dB bandwidth of 16.5GHz. Clearly-opened eye diagrams for a 20Gbit/s 1.5 mu m optical data stream have been demonstrated.

The capacitive charge transient measurement technique generates laterally resolved two-dimensional resistivity topograms of wafers with diameters up to 150 mm. The method is applicable to semi-insulating substrates with resistivities between 10/sup 6/ and 10/sup 9//spl Omega/cm. The range and characteristic lateral patterns of homogeneity variations in substrates of different vendors will be addressed, including LEC GaAs, VB GaAs and LEC InP. The effect of annealing treatments and interrelations between electrical and optical topograms will also be discussed.

The temperature Te of photoexcited carriers in semi-insulating GaAs wafers is determined with high lateral resolution by topographic measurement of the spectrally selected band-to-band recombination luminescence intensity IPL. It is also calculated from a detailed balance between carrier excitation and recombination, taking into account optical phonon, electron-electron, piezoelectric, and acoustic phonon scattering processes. Comparison of the experimental and theoretical Te data yields the lifetime τ of the photoexcited carriers, which is thus obtained without time-resolved measurement. The lifetime results are corroborated by comparison of the measured and calculated dependence of Te on the laser excitation power. The relation between Te and τ for given excitation power allows for the generation of two-dimensional high-resolution lifetime topograms. The correlation with conventional IPL topograms is direct, duplicating the lateral cellular pattern with comparable fluctuation amplitude. From these properties, it is inferred that τ is dominantly determined by inhomogeneously distributed nonradiative recombination centers. Their concentration is low in the walls of the dislocation network and high in the interior of the cells. The statistical evaluation of Te topograms allows for an application-oriented comparison of the quality and homogeneity of GaAs wafers.

The characterization of III-V compound semiconductor substrates and epitaxial layers with photoluminescence imaging is reviewed. The luminescence patterns of semi-insulating GaAs are dominantly determined by the concentration and distribution of nonradiative recombination centers, as shown by comparison with spectroscopic temperature and lifetime topography of photoexcited carriers. Wafers fabricated with various growth and annealing procedures are evaluated. Presently available informations on nonradiative centers in GaAs are summarized and discussed. The correlation of luminescence, absorption and resistivity topograms of InP substrates shows various interrelated influences of the Fe acceptor distribution. High resolution luminescence images of growth induced, strain induced and substrate induced defects in epitaxial heterostructures are obtained. The generation of relaxation dislocations in pseudomorphic layers is influenced by growth parameters, layer structures, layer doping and also by substrate properties. Nonradiative recombination center patterns replicate the arrangement of threading dislocations in the substrate.

Low-temperature photoluminescence topography has been used to monitor local variations in composition of In1-yGayP and AlxGa1-xAs layers which were grown lattice-matched on semi-insulating LEC GaAs substrates by MOCVD. Whereas the in content varies by less than +or-1% over the whole 2 inch water, the Al concentration changes by about +or-3%. In AlxGa1-xAs/GaAs quantum well (QW) structures the dependence of photoluminescence energy on QW thickness is used to estimate spatial variations in the thickness of the well material. The resulting thickness topogram is compared with numerical simulations of the gas flow profile in the MOCVD reactor.

Spectrally and spatially resolved low-temperature photoluminescence topography has been applied to investigate the lateral variation of impurities in nominally undoped epitaxial GaAs layers. The concentrations of both shallow donors and acceptors exhibit lateral variations. The donor variation pattern appears to be arbitrary, but the fluctuation of shallow acceptor carbon clearly reproduces the well-known cellular structure of the liquid encapsulated Czochralski GaAs substrate dislocation density distribution, suggesting that the carbon incorporation into the epitaxial layer is influenced by the substrate during the growth of metalorganic vapor phase epitaxy.

High-resolution photoluminescence topography of GaAs at 300 and 2 K is reported. Topics include lateral homogeneity of semi-insulating substrates, quality of surface polishing, evaluation of sheet carrier concentrations and optimization of implant activations. Spectrally resolved low temperature topography allows images to be generated of carrier temperature and lifetime in substrates and of quantum well thickness variations in heterostructures.

A method based on time-dependent measurement of charge transients has been developed to evaluate the specific resistivity of semi-insulating wafers quickly, non-destructively and with good lateral resolution. The material is inserted between capacitive electrodes. The time-dependent charge distribution after application of a voltage step allows evaluation of the resistivity with high accuracy in the range 10(6)-10(9) OMEGA-cm. The technique has been elaborated to allow rapid contactless scanning of wafers for routine measurement of the lateral variation of resistivity with a resolution of about 2 mm2. The results are in agreement with conventional Hall measurements. The mechanical and electronic systems are described in detail. Scans across wafers cut from as-grown as well as annealed ingots are presented.

The variation of material properties along the growth axis of single crystal LEC GaAs ingots is studied. Parameters investigated include concentration and lateral variation of EL2, photoluminescence intensity, resistivity, the concentration of extrinsic shallow acceptors and, after test implantation, the sheet resistivity. Correlations between the observed trends are identified and discussed in terms of compensation and segregation. In general, a very satisfactory homogeneity is found. Remaining variations are identified and evaluated with respect to their device-relevant consequences.

The temperature of photoexcited electrons in LEC-grown semi-insulating GaAs is determined by photoluminescence spectroscopy at low temperature. From the electron temperature the carrier lifetime is calculated. We report two-dimensional high resolution (50-mu-m) temperature and lifetime topography of wafers with different annealing history. A strict correlation is found between lifetime and luminescence intensity. The electron temperature and its spatial variation are strongly modified by annealing and are thus useful quality criteria for a quantitative comparison.

The spatial distribution of residual shallow acceptors in undoped semi-insulating GaAs has been studied quantitatively by electronic Raman scattering with a spatial resolution of ∼50 μm. This acceptor distribution has been correlated with the spatial distribution of the compensating EL2 donor in its neutral charge state measured by near-IR absorption topography. An enhanced acceptor concentration is found in regions which show high-IR absorption: From the comparison with low-temperature cathodoluminescence results, it is found that the intensity of the band-to-acceptor recombination normalized to the band-to-band luminescence intensity reproduces the acceptor distribution measured by Raman scattering. Implications of the present result on the compensation model for undoped semi-insulating GaAs are discussed.

It is demonstrated that ion implanted layers can be analysed prior to annealing by measuring the sub-bandgap optical absorption of the damaged lattice. The absolute value and lateral homogeneity of the implantation dose can be measured. The method is fast, nondestructive and compares favorably with existing measurement techniques.

Electron paramagnetic resonance studies on as-grown semi-insulating liquid encapsulation Czochralski (LEC) GaAs at 35 GHz have revealed a new resonance labeled FR3. It is consistently present in LEC material but usually unobservable in Bridgman samples, thus strongly indicating that the defect involved contains boron. The center has trigonal symmetry and is electrically active. Its spectrum indicates a d 9 or p5 one-hole configuration. We tentatively identify FR3 with a Ga antisite complex, Ga−As -B0Ga.

Two-dimensional mapping of band-edge photoluminescence and infrared absorption has been carried out at room temperature on 50 mm SI GaAs wafers. The spatial resolution was either 215 or 50 μm depending on the seize of the topograph, the recording time of one topograph was 30 s for the infrared absorption and about 10 min for the photoluminescence. The topographs show a remarkable correspondence in the macroscopic features (“W” shaped profile) as well as in the fine cellular structures: areas of large absorption exhibit large luminescence intensity. It is concluded that this is due to a spatially inhomogeneous compensation of acceptor states by EL2 midgap levels. The two topographical methods can be used in combination to assess the bulk inhomogeneities as well as the surface quality of wafers.

The photoresponse of the As+Ga antisite electron-paramagnetic-resonance (EPR) has been studied in as-grown semi-insulating GaAs as a function of illumination time and photon energy hν. The As+Ga EPR signal intensity changes are nonmonotonic in time in the range 1.1≲hν≲1.4 eV. The spectral dependences of As+Ga enhancement and quenching show distinct similarities with the EL2 optical cross sections σ0n (hν) and σ0p (hν), respectively. These results demonstrate that the EL2 defect and the AsGa antisite have practically identical optical and photoelectronic properties.

Ytterbium-doped InP emits a characteristic luminescence band near 1.0 \ensuremath{\mu}m, arising from intra-4f-shell transitions of ${\mathrm{Yb}}^{3+}$(4${\mathrm{f}}^{13}$). A Zeeman analysis of the complex set of emission lines, in magnetic fields up to 22 T, reveals that the spectrum arises almost entirely from only one type of cubic Yb center, presumably on a substitutional cation site.

A new technique for recording spatial fluctuations of the optical absorption in GaAs slices is reported. It is based on a commercially available linear silicon diode array which monitors the optical absorption attributed to the omnipresent deep trap named EL2. Because this technique gives quantitative results, displays excellent spatial resolution (200 μm for 2-in. wafers), and is fast, it appears to be highly useful for wafer characterization and quality control.

The photo-response of the ASGa+ antisite electron-paramagnetic-resonance (EPR) has been studied in as-grown GaAs as a function of illumination time and photon energy. The results establish a firm and positive correlation between ASGa and the deep donor level EL2. Spatially resolved EPR measurements show that the ASGa+ concentration can fluctuate by about a factor of two across a 2-inch semiinsulating GaAs wafer.