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Erbium (Er) doped semiconductors are of interest for light-emitting device applications operating at around 1.55 μm and for the potential integration with other semiconductor devices. However, the optical emission of Er3+ ions in semiconductors has not been as efficient as in dielectric materials, particularly at room temperature. This may be because ionic bonds, which are characteristic of dielectrics, are better suited for forming the required Er3+ energy levels than are covalent bonds, which are present in most III-V semiconductors. In this paper, we report 1.55 μm emission from an Er-doped GaN LED. We also discuss the effect of the measurement temperature on the emission spectrum as well as the effect of sample annealing on the emission spectrum.

We report on a magnetophotoluminescence study of an n-type modulation doped ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}{\mathrm{As}\mathrm{ }(\mathrm{Si})/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}\mathrm{ }(\mathrm{Si})$ quantum-well structure in which a dense electron gas populates the AlAs X valleys. The interband transitions in this system are type II and exhibit GaAs and AlAs LO-phonon replicas. In the presence of a magnetic field applied perpendicular to the structure's layers luminescence features associated with the l=0 and l=1 Landau levels of the AlAs ${X}_{z}$ valleys were resolved. The slope $dE/dB$ of these transitions yield an in-plane effective mass ${m}^{*}$ of 0.44.

High‐quality In0.53Ga0.47As epilayers have been grown on semi‐insulating (100) Fe‐doped InP substrates. The growths were performed by liquid phase epitaxy (LPE) using rare‐earth‐doped melts in a graphite boat. The rare‐earth elements studied were Yb, Gd and Er which act as gettering agents of impurities. Hall measurements show an elevated electron mobility for rare‐earth‐treated samples over undoped samples, μe=11 470 cm2/V s at 300 K and reduced carrier concentration (n‐type), 9.33×1013 cm−3. The Hall results indicate an improvement in layer quality, but suggests that the treated layers are compensated. Photoluminescence (PL) studies show that the layers grown from rare‐earth‐doped melts have higher integrated PL efficiency with narrower PL linewidths than the undoped melt growths. The grown materials were fully characterized by Fourier transform infrared spectroscopy, double‐crystal x‐ray diffraction, energy dispersive spectroscopy, secondary‐ion‐mass spectroscopy, and deep level transient spectroscopy ...

A technique of impurity‐free vacancy‐induced disordering of GaAs/AlGaAs multiquantum wells (MQW) that is area selective, very reliable, and highly reproducible, has been developed. The localized compositional disordering is induced by rapid thermal annealing of the sample after it has been coated with a thin film of ‘‘spin‐on’’ glass and prebaked at 400 °C in a high purity nitrogen:oxygen (78:22) atmosphere. In order to self‐consistently determine the diffusion coefficient of the Al and Ga atoms, the photoluminescence peak is fitted to the n=1 electron to heavy hole transition that corresponds to an error function potential profile caused by the diffusion. The process has been used to integrate two optical devices on a MQW structure. One is a nonlinear directional coupler all‐optical switch, and the other is an integrated Mach–Zehnder all‐optical modulator. The switching characteristics of the devices were measured using the conventional pump‐probe measurement technique.

We confirm that as the misfit strain in pseudomorphic epitaxial layer increases, surface thermodynamics controlled growth modes can change from a layer-by-layer to a three-dimensional (3-D) island mode. Both in-situ reflection high energy electron diffraction studies and in-situ scanning tunneling microscopy studies are utilized to demonstrate this transition to 3-D growth. This concept allows one to grow GaAs/InxGa1-xAs/GaAs heterostructures where the electrons in InxGa1-xAs are possibly confined in lower dimensions.

The photoinduced bleaching and blueshift of the lowest heavy-hole-like exciton in an anisotropically strained multiple quantum well exhibits a large enhancement for femtosecond light pulses polarized parallel to the axis of maximum compressive strain relative to those measured using orthogonally polarized light. These results imply that the strain-induced anisotropy in $k$ space leads to exciton-exciton interactions which possess a strong dependence on the orientation with respect to the strain axis, relative orientation, and spatial extent of the photogenerated excitonic dipoles.

A variable-strain quantum-well semiconductor heterostructure has been designed and studied. Mutually opposite slopes for heavy- and light-hole band edges are obtained by grading the strain within the quantum well from compressive to tensile. A simultaneous red and blue quantum-confined Stark shift for the heavy- and light-hole transitions, respectively, and a unique bias-controlled crossover have been observed by modulation spectroscopy. This indicates that the heavy and light holes experience opposite fields created by the same strain at the same location.

The pump-probe technique was employed in the study of excitonic optical non-linearities at 40 K in a GaAs/Al0.1Ga0.9As multiple quantum well under thermally induced in-plane uniaxial strain. We report the first observation of an ultrafast large-angle polarization rotation of the probe light effected by the bleaching of the anisotropic absorption near the heavy hole exciton peak in this material. Dynamic rotations as large as 42° have been measured for a compressive strain of ~ 0.2%. In addition, a dependence of the phase space filling produced by resonantly excited excitons on the orientation of the pump polarization vector has been observed which decays with a time constant of 0.5 ps. This decay is attributed to the ionization of excitons into free electron-hole pairs. The subsequent decline of the probe rotation is governed by the removal of these carriers from the wells.

We propose and demonstrate mode locking of a novel dual-gain-media Nd:fluorophosphate and Nd:silicate glass laser. It overcomes the linewidth limitation of a single-medium Nd:glass laser. A pulse bandwidth of 41 nm has been obtained, which is nearly twice as broad as that from a single-medium Nd:glass laser. Wing-free pulses of 38 fs have been generated, which are the shortest from a Nd:glass laser oscillator.

Low-temperature (4.2 K) magnetoreflectance measurements have been performed on a series of In x Ga 1-x As/Al y Ga 1-y As strained-layer quantum wells (QW's) with the InAs mole fraction x varying from 0 to 0.2, for three different well widths, and for the magnetic-field range of 0-9 T. The diamagnetic shift data of 1s, 2s, 3s,... excitons are fit to a theoretical model to determine the exciton binding energies and the in-plane reduced effective masses, which are presented as a function of x, for excitons in 80, 120, and 340 A In x Ga 1-x As/Al y Ga 1-y As QW's. In the case of high-barrier QW's, the binding energies and effective masses appear to decrease linearly with increasing x over the range studied

The effect of thermally induced in-plane uniaxial strain on the optical properties of a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple quantum well (MQW) has been studied in detail. The strain was produced by bonding the MQW thin films to ${\mathrm{LiTaO}}_{3}$, a transparent substrate which possesses a direction-dependent thermal expansion coefficient. At temperatures different from the bonding temperature we have observed an anisotropy in the optical properties of the MQW due to the strain-induced lowering of its in-plane fourfold rotation symmetry. The anisotropic absorption and birefringence for light incident normal to such a MQW structure have been determined and compared to a theory involving the mixing of the valence subbands.

An extensive photoreflectance (PR) study has been done on a series of undoped and n‐type, InGaAs and InAlAs molecular beam epitaxy (MBE) grown layers with different In mole fractions, and epilayer thicknesses on Fe‐doped semi‐insulating (SI)‐InP substrates. Three substrate features were observed in the spectra. From investigations of the temperature dependence, time constant dependence, and an additional cw light beam intensity dependence, they were identified as an excitonic transition from the substrate, a free electron transition near the interface which gives a Franz–Keldysh oscillation, and a transition from the spin–orbit split‐off valence band. The Franz–Keldysh effect indicates that a temperature dependent built‐in electric field is formed near the interface. The dependence of the field on doping concentration, strain, or epilayer composition (band gap) was insignificant. The PR signal from a SI‐InP wafer after a pre‐MBE‐growth heating was found to be strongly enhanced over that from an untreated ...

Magnetoreflectance studies on GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells grown on (111) and (001) substrates have been performed in magnetic fields from 0 to 9 at 4.2K. Excitonic transitions of 1s, 2s, 3s, . . . states are observed and identified for the transitions from the first heavy-hole subband to the first electron subband and from the first light-hole subband to the first electron subband in the well. From the diamagnetic shifts, we have determined the reduced effective masses, ${\mathrm{\ensuremath{\mu}}}_{\mathrm{\ensuremath{\perp}}}$, and the binding energies for excitons in the well using several different methods. A comparison of the reduced masses of the excitons in the (111) and (001) samples determined experimentally gives a ratio of ${\mathrm{\ensuremath{\mu}}}_{111\mathrm{\ensuremath{\perp}}}$/${\mathrm{\ensuremath{\mu}}}_{001\mathrm{\ensuremath{\perp}}}$=0.92. We have also attempted to deduce the heavy-hole and light-hole effective masses perpendicular and parallel to the (111) axis, and the band parameters.

The authors have studied, both theoretically and experimentally, the effects of biaxial strain upon the performance characteristics of broad-area InP-InGaAsP-In/sub x/Ga/sub 1-x/As (0.33 >

Reflectance and photoluminescence spectroscopy have been used to study the optical properties of high quality InxGa1−xAs/GaAs (0.13≤x≤0.30) single quantum wells. The results show strong agreement with the theoretical model used taking into account the strain potential. The agreement of the theoretical model, though, deviates from the experimental results for large values of excess strain in the well. For the case of the large strain (x=0.30) the reflectance indicates the strain in the well is hydrostatic rather than biaxial. The relevance of this fact is discussed in relation to device performance.

We demonstrate a lossless 1/spl times/2 optical switch utilizing resonant vertical coupling between an active and a passive waveguide. Optical power is coupled into the passive waveguide and split into two ports using a 3-dB Y-junction splitter. The mode is then coupled up to a 1-mm-long active waveguide where gain is provided. A 100-/spl mu/m-long taper is utilized in each arm for coupling the mode from the passive to the active waveguide. Internal gain greater than 22 dB is obtained in each arm of the integrated splitter. High yield and good uniformity of devices are obtained over multiple processing runs.

The effects of biaxial compressive and tensile strain on the excitonic resonances and associated changes in refractive index and electro‐optic effect in quantum wells have been calculated and measured. Theoretical calculations include the important heavy‐hole–light–hole band mixing effects. It is seen that the excitonic contributions dominate near the band edge. With increasing compressive strain the linear electro‐optic effect is slightly increased, while the quadratic effect is greatly enhanced. The effects are reversed in quantum wells under tensile strain.

We have measured the narrowest half‐width at half‐maximum photoluminescence linewidth of 2.8 meV, in 40‐period lattice‐matched In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells, grown by molecular‐beam epitaxy with growth interruption. A simple analysis of the linewidth suggests that the structure has near perfect interfaces. Temperature‐dependent photoluminescence linewidth data indicate impurity incorporation due to the growth interruption. However, the high quality of the multiple quantum well is not impaired as is seen in the room‐temperature absorption data, where excitonic features up to n=3 sublevel are clearly seen. Carrier lifetime in this multiple‐quantum‐well system has been measured, we believe for the first time, using the picosecond photoluminescence correlation technique. A lifetime of 860 ps is obtained, which is similar to the value obtained for high‐quality GaAs/AlGaAs and In0.53Ga0.47As/InP quantum wells. This further confirms the high quality obtained in this ternary material system...

We propose and demonstrate a novel expanded mode voltage controlled optical switch based on electrorefraction and electroabsorption in resonantly coupled tapered vertical waveguides. The device was grown in a single standard epitaxial growth and was processed using conventional fabrication techniques. A 200-/spl mu/m-long mode transformation region was used for expanding the mode and optical switching. Greater than 20-dB switching contrast ratio was obtained with a reverse bias of less than 1 V. Reduced far-field divergence angles (8/spl deg//spl times/24/spl deg/) were also achieved. With good contrast ratio at low voltage bias and an inherent expanded mode, this device shows promise for low-cost optoelectronic switching applications.

We fabricated a multiple-quantum-well waveguide modulator incorporating two tensile S-strained layers, within a nominally lattice matched well, that act to provide bias-independent Stark shift for both the light and heavy holes. We report results for two waveguide geometries. One is a 2.3-/spl mu/m-wide ridge single-mode waveguide that was deep-etched 0.7 /spl mu/m below the active region to ensure that the confinement factor for both the TE and TM modes are nearly equal. The other was a broad-area (slab) multimode waveguide. For both geometries, transmission measurements indicate polarization insensitivity within 3 dB for 2.5 V of reverse bias over the 1.600-1.630-/spl mu/m wavelength range.

We have examined the growth and device characteristics of In0.53+x Ga0.47−x As/ In0.52 Al0.48 As (0≤x≤0.27) pseudomorphic modulation‐doped field‐effect transistors on InP substrates. In situ reflection high energy electron diffraction oscillation studies were carried out to study the growth of pseudomorphic InGaAs on GaAs and InP substrates. The data from these measurements and a theoretical formalism based on energy minimization suggest that in the pseudomorphic growth regime increased strain causes growth modes to change from two‐dimensional layer‐by‐layer to a three‐dimensional island mode. The resulting interface roughness is used as a parameter to explain the observed trends in channel mobility and device performance. It is also shown that altered growth techniques, such as migration enhanced epitaxy, in which the surface reconstruction may be changed, can restore the layer‐by‐layer growth mode for large amounts of strain in the pseudomorphic layer.

A new class of measurements on GaAs quantum well structures based on frequency domain nonlinear laser spectroscopy is described. Room temperature measurements of the excitation relaxation show an interference effect in the lineshape which is interpreted as a shift in exciton frequency. Low temperature measurements on the localized exciton provide an excitation lineshape which eliminates the effects of inhomogeneous broadening and shows the presence of spectral diffusion.

Deep‐level transient spectroscopy measurements have been made on molecular‐beam epitaxial In0.53(GaxAl1−x)0.47As lattice matched to InP. Several electron and hole traps, with activation energies ranging from 0.14 to 0.79 eV, have been identified and characterized. In particular, systems of electron traps (0.30≤ΔET≤0.79 eV) and hole traps (0.14≤ΔET≤0.31 eV) with monotonically changing activation energies have been identified in these alloys. We believe these traps are dominant in this alloy system.

The well known quantum confined Stark effect (QCSE) is currently being exploited to design optoelectronic devices based on electric field controlled absorption of photons. QCSE is also responsible for strong below exciton resonance changes in refractive index with applied field. These changes can be used for high speed couplers and switches in waveguides. This paper focuses on the use of strain to influence the excitonic resonances in In x Ga 1− x As/Al 0.2 Ga 0.8 As and In 0.53± x Ga 0.47∓ x As/InGaAsP multiple quantum wells. Experimental results are presented showing the effect of compressive and tensile strain on the refractive index changes. Theoretical results including the important HH-LH band mixing effects are presented for the electrooptic effect. In particular, the contribution of the excitonic part is discussed and is found to dominate the electro-optic effect near the bandedge.

We present a type of strained semiconductor quantum-well structure that exhibits bias-independent heavy- and light-hole degeneracy. This effect is achieved by inserting thin layers of highly strained material in an unstrained quantum well. By adjusting the thickness and the position of the highly tensile strained layers, the quantum confined Stark effect for the heavy and light holes can be engineered separately to control the bias dependent polarization properties. Experimental results on such a structure agree well with the theory. These unique bias-dependent polarization properties have important applications in optoelectronic devices when specific polarization properties are required.

Ultrafast all-optical switching has been demonstrated in a Y-junction waveguide device fabricated on a GaAs-AlGaAs multiple quantum well structure. The mechanism responsible for switching is attributed to the optical Stark effect which enabled consecutive switching events spaced 1.7 ps apart. Carrier generation due to linear absorption of the band-tail states and the observed two-photon absorption results in a gradual slope in the background. Our experiments indicate that nonlinear refraction due to the AC Stark effect is most pronounced when the excitation field is polarized with the E-field parallel to the interfaces.

We have designed and studied a new type of strained semiconductor quantum well structure, variable‐strain quantum well. The strain within the quantum well is graded from compressive to tensile in order to obtain mutually opposing slopes for the heavy‐ and light‐hole band edges, causing the heavy and light holes to experience opposite fields created by the same strain. A unique bias controlled crossover with a simultaneous red and blue quantum confined Stark shift for the heavy‐ and light‐hole transitions, respectively, has been observed by electroreflectance spectra. This results in a bias controlled change of the polarization properties and the transition energies suitable for polarization controllable photonic devices.

A nonlinear switch formed by the integration of an overmoded multi‐quantum‐well (MQW) section with disordered input and output branching waveguides is presented. The area‐selective disordering of GaAs/AlGaAs MQWs is achieved by diffusion of group III vacancies generated by etching of the surface oxide. The absorption edge of the disordered MQW regions was shifted by 71 nm and the disordered ridge waveguides had a loss figure of 8 dB/cm. Time‐resolved optical pump‐probe measurements were performed on an integrated switch that had more than a 5:1 power split between the two output ports. The measured signal recovery of the switch had a time constant of 110 ps.

Summary form only given. Hybrid lasers provide a new way to utilize the useful properties of different laser media to control and to improve laser performance. Nd:glass has a broad linewidth and can produce less than 100 fs pulses. Due to its partially inhomogeneous broadening, its lasing spectrum is often not well shaped and stable. It was demonstrated in an actively mode-locked hybrid Nd:phosphate glass and Nd:YLF laser that a small gain from Nd:YLF can stabilize the lasing spectrum and Nd:phosphate glass facilitates more easily spectral broadening, producing coherent and short laser pulses. We have demonstrated that a gain from Nd:YVO/sub 4/ can also exert effective control of Nd:phosphate glass lasing spectrum in a diode-pumped CW hybrid Nd:phosphate glass and Nd:YVO/sub 4/ laser, even when the line centers of the two laser media separate by as far apart as 10 nm. In the paper we report passive mode locking of a diode pumped, hybrid Nd:phosphate glass and Nd:YVO/sub 4/ laser.

980-nm substrate-emitting oxidized-aperture VCSELs with threshold currents in the 150 /spl mu/A to 500 /spl mu/A range have been developed for optoelectronic interconnects. 8/spl times/8 VCSEL arrays with 125 /spl mu/m pitch have been flip-chip bonded to CMOS driver circuitry having 0.5 /spl mu/m gate size. InGaAs/InP 8/spl times/8 detector arrays have been flip-chip bonded to provide good responsivity and high speed detection in dense arrays with 125 /spl mu/m pitch. Data rates as high as 1.1 Gb/s have been demonstrated with the incorporation of refractive coupling optics between transmitter and receiver arrays. Studies have been conducted of crosstalk and alignment sensitivity of these optoelectronic interconnect arrays. Design and modeling techniques have been demonstrated for the development of diffractive optics for optoelectronic interconnects. Special techniques have been developed to deal with very short working distances and subwavelength feature in the diffractive optics. Fan-out performance up to 7/spl times/7 with accurately controlled intensity weights has been demonstrated with diffractive optics. The use of diffractive optics in optoelectronic interconnects with fan-out and/or fan-in can make the interconnect an integral part of the optoelectronic processing algorithm.

Summary form only given. The performance of multiple quantum well (MQW) electroabsorption (EA) waveguide modulators based on the quantum confined Stark effect (QCSE) shows considerable promise due to the low drive voltage, enhanced excitonic absorption, and high-speed operation. Our approach uses a unique quantum well design that incorporates two thin highly tensile strained GaAs-strain layers in order to provide separate confinement, and effective well widths denoted L/sub lh/ and L/sub hh/, for the LH1 and HH1 wavefunctions respectively. This design maintains the degeneracy of the LH1 and HH1 energy levels, for polarization independent transmission, for potentially larger values of the electric field as compared to other approaches.

We have demonstrated an ultra-compact, highly efficient mode transformation between a highly confined active waveguide and a well-confined passive waveguide using conventional fabrication and single epitaxial growth. The mode is transformed over a taper 100 /spl mu/m long and with a low round trip mode transformation loss of 0.3 dB. This scheme provides an attractive platform technology for monolithic integration of various active and passive devices, like splitters with amplifiers, Mach-Zehnder interferometers etc.

Monolithic integration is crucial for the development of optoelectronic integrated circuits that offer higher functionality than discrete devices. One of the main requirements in the implementation of any integrated circuit is the ability to address different parts of chip either electrically or optically. For electro-optic devices, these different areas need to be electrically isolated from one another. One approach that is routinely used in the semiconductor industry is the proton implantation, which very effectively produces high resistivity material for the electrical isolation. However, the process also leads to defects that are harmful to the performance of active optoelectronic devices. In this work, we report the use of selective zinc indiffusion in n-type semiconductors as a viable method of creating isolated islands of p-n junctions. We used this process to fabricate a symmetric integrated Mach-Zehnder modulator in which only one arm is subjected to an applied electric field for electro-optic modulation. In our initial device a 10dB contrast ratio was attained with about 5V reverse bias.

Results of calculations on how band-structure changes introduced by strain affect the gain spectra in multi-quantum-well (MQW) lasers are presented. Reduction of threshold injection as well as increased TE mode emission occurs for the compressive-strain case. In tensile strain the thresholds for TE and TM modes approach each other. Experimental studies on the compressive-strain laser structures show that the spontaneous and lasing spectra shift to longer wavelengths, the threshold current density is reduced, and a more rapid rise of gain with increased injection occurs. The output spectrum shifted from the 959-962 nm range for the GaInAs devices with 20% In to the 1033.5-1041.0-nm range for devices with 30% In. The threshold current density decreased with increasing strain, as expected from the theory. The modal gain of the devices and the peak modal gain were shown to rise very quickly with increased injection. This qualitatively agrees with the expected decrease in hole density of states brought about by strain, which could cause the hole states to be more rapidly filled and result in a more rapid rise in the material gain. >

We report a novel approach to the design of normal incidence multiple quantum well light modulators. The quantum confined Stark effect is utilized to tune the light polarization rotation and phase retardation created by a thermally induced in-plane anisotropic strain. An exceedingly high contrast ratio of 5000:1 is demonstrated for a normally-on device at room temperature. >

A multiple quantum well modulator was fabricated using epitaxial lift-off techniques and bonded to a transparent substrate which possesses a direction-dependent thermal expansion coefficient. The modulator utilized the quantum confined Stark effect to tune the phase retardation and polarization rotation created by the thermally induced in-plane anisotropic strain. A contrast ratio of 7000:1 was achieved in an electrically controlled multiple quantum well light modulator. >

We report femtosecond optical switching in a strip-loaded Y-junction device fabricated on a multiple quantum well (MQW) structure. The MQW heterostructure consisted of 38 periods of GaAs-Al/sub 0.3/Ga/sub 0.7/As quantum well and barrier layers. The Y-junction switch can function as an optical multiplexer/demultiplexer in time division multiplexed (TDM) systems as well as a key component for matrix switches in asynchronous transmission mode (ATM) network systems. A comparison of the switching behavior on the orientation of the control pulse polarization has also been undertaken and the results are discussed.

Theoretical studies of the effects of biaxial strain on the performance of InP/InGaAs/InGaAsP multiple quantum well separate confinement heterostructure (MQW-SCH) lasers are discussed. The devices are found to exhibit characteristics that agree with predicted trends. No minimum in the threshold density curve has been found. The best devices exhibited threshold current densities of 689 A/cm/sup 2/, internal quantum efficiencies of approximately unity and loss coefficients of approximately 5.6 cm/sup -1/. >

An investigation of the properties of discrete and integrated InP-based strained In/sub x/Ga/sub 1-x/As-InP (0.33 >

Ultrafast all-optical switch-on and switch-off of GaAs-AlGaAs MQW waveguide devices that employ carrier induced nonlinearities in quantum wells is reported 2 ps consecutive all-optical switching due to the optical Stark effect has also been observed.

The frequency response of multi-quantum well (MQW) optoelectronic devices is governed by the rate of carrier injection and removal from the active regions. In a conventional p-i-n structure vertical rate limiting carrier transport mechanism is primarily due to thermionic emission of holes and electrons from the quantum wells. However, in waveguide structures the p and n contacts can be in-diffused on either side of the waveguide. With an applied reverse electrical bias, lateral transport of the carriers by diffusion and drifting is accomplished without the need to overcome any energy potential barrier. Since the waveguide geometry can be very small (/spl sim/1 /spl mu/m), the time taken for the carriers to traverse that region is inherently fast and hence high speed devices can readily be achieved.

High quality In/sub 0.53/Ga/sub 0.47/As has been grown on semi-insulating (100) InP:Fe substrates. The growths were performed with rare-earth (Er, Gd, and Yb) doped liquid phase epitaxial (LPE) growth melts in a graphite boat. Hall measurements show improved electron mobility and reduced (n-type) carrier concentration. Photoluminescence (PL) shows rare-earth doped layers have a higher PL efficiency with narrower linewidths than undoped layers. However, two deep levels are created by the rare earth elements. The grown samples were also characterized by FT-IR, double crystal X-ray diffraction, EDAX, SIMS, and DLTS.

Ultrafast all-optical demultiplexing will be needed to handle optical time domain multiplexed signals in excess of 40 Gb/s. We report a symmetric Mach-Zehnder all-optical switching device that is fabricated using GaAs/AlGaAs multiple quantum well structures and selective area quantum well disordering for the integration. Although the switching is based on carrier-induced nonlinearities, by employing two consecutive control pulses, one to switch the device on and the other to switch the device off, the switching speed is not restricted by the slow carrier relaxation time.

A novel optically addressed normal incidence multiple quantum well light modulator based on polarization rotation has been demonstrated for the first time. This modulator employs the anisotropic excitonic absorption created by a thermally induced in‐plane uniaxial strain in a multiple quantum well structure to achieve rotations as large as ±25°. An exceedingly high contrast ratio of 330:1 has been measured in this device.

The dielectric function of a thick layer of In(0.52)Al(0.48)As lattice matched to InP was measured by variable angle spectroscopic ellipsometry in the range 1.9-4.1 eV. The In(0.52)Al(0.48)As was protected from oxidation using a thin In(0.53)Ga(0.47)As cap that was mathematically removed for the dielectric function estimate. The In(0.52)Al(0.48)As dielectric function was then verified by ellipsometric measurements of other In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As structures, including (MODFET), and is shown to provide accurate structure layer thicknesses.

The Fermi level position in low temperature (LT) GaAs has been studied by photoreflectance (PR). By etching the LT‐GaAs to a different thickness, we find the Fermi level in the as‐grown as well as the annealed LT‐GaAs is firmly pinned. The pinning position, however, occurs at different energies: 0.47 eV below the conduction band edge for the as‐grown samples and 0.65 eV below the conduction band edge for the annealed samples. The pinning in the as‐grown LT‐GaAs is believed to be the result of a high degree of charge compensation by deep levels, while the pinning in the annealed LT‐GaAs is due to the depletion of carriers by the Schottky barrier at the metallic As precipitates. From the measured Fermi level and ionization ratio of As antisites, the (0/+) donor level of the As antisite in LT‐GaAs is, for the first time, determined at Ec−0.57 eV.

Room‐temperature photoluminescence is used to investigate the basic recombination mechanisms in carbon‐doped GaAs samples, with hole concentrations ranging from 3.0×1016 to 1.2×1020 cm−3. The solution of a one‐dimensional, steady‐state continuity equation for minority carriers indicates that in heavily carbon‐doped GaAs, surface recombination is minimal, while bulk nonradiative recombination is dominant. The bulk nonradiative recombination rate depends not only on p2, which represents Auger recombination, but also on p3. By using a single p+‐GaAs:C (1×1020 cm−3) base layer in an AlGaAs/GaAs heterojunction bipolar transistor, the surface recombination is minimized.

A systematic study of the structural quality and arsenic content of as‐grown In0.52Al0.48As/InP layers deposited on InP by molecular beam epitaxy at temperatures between 150 and 450 °C was performed using transmission electron microscopy and particle‐induced x‐ray emission. We found that the amount of As incorporated in the layers generally increases with decreasing growth temperature, with the crystalline quality of the layers being good at growth temperatures higher than 200 °C. At 150 °C, a large density of pyramidal defects is formed, the defects are related to the very large amount of excess As incorporated into the layer. The mechanisms leading to the formation of these defects are discussed. At 200 °C, however, the amount of excess As is lower than expected, and wavy streaks of diffuse scattering are seen in electron diffraction. It is shown that small ordered domains of the CuPt type on the group III atoms are responsible for these features.