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We demonstrate low‐loss optical mode‐size tapers in InGaAsP/InP optical waveguides fabricated by selective organometallic chemical vapor deposition. The tapers increase the vertical mode size by ≊300%. Taper losses as low as 0.4 dB (on‐chip, excluding coupling) were achieved, with 2.6 dB coupling loss to a flat‐end, single‐mode fiber at 1540 nm wavelength.

The recombination kinetics of the quasi‐one‐dimensional (1D) carriers confined in quantum wires grown by organometallic chemical vapor deposition on nonplanar, patterned substrates is reported for the first time. Due to the small (240 nm) wire spacing, excited carriers are efficiently captured into the wires on a sub‐ps time scale. The radiative recombination lifetime of the captured 1D carriers is longer than 310 ps. Time‐resolved cathodoluminescence spectra directly monitor thermalization of the carriers within the wire.

Arsenic dimers and multilayers are shown to exist on (001)GaAs surfaces under atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) conditions. We obtained reflectance‐difference spectra from surfaces in AP H2 that are equivalent to those obtained from the (2×4) and disordered‐c(4×4) reconstructions prepared in ultrahigh vacuum by molecular beam epitaxy. Implications for models of OMCVD growth.

Luminescence properties of GaAs/AlGaAs quantum wire (QWR) heterostructures grown by organometallic chemical vapor deposition on V‐grooved substrates are reported. A model of the crescent‐shaped wires yields parabolic QWR potential wells with subbands separated by 21.7, 3.9, and 16.7 meV for electrons, heavy holes, and light holes and effective width of 16 nm for the ground electron state. Spectrally and spatially resolved cathodoluminescence images reveal highly uniform emission from the QWR regions. Photoluminescence excitation spectra exhibit enhanced absorption at the QWR subbands, with subband separations in good agreement with the model.

We determine types and concentrations of free carriers in GaAs layers under organometallic chemical vapor deposition growth conditions from the linear electro‐optic structure observed near 3 eV in reflectance‐difference spectroscopy. The sensitivity is about 1017 cm−3 at 400 °C and 1018 cm−3 at 600 °C, sufficient to measure common doping levels at or near growth temperatures. We observed the transition between n‐ and p‐type doping during atomic layer epitaxy of a carbon‐doped p‐type layer on an n‐type substrate at 470 °C.

We report the observation of two photon absorption which is strongly dependent on the applied electric field and the optical polarization. At 1.55 μm wavelength, the two‐photon absorption coefficient of the GaAs/AlGaAs multiquantum well (MQW) waveguides for transverse‐magnetic light is about seven times lower than for transverse‐electric polarized light and changes by a factor of approximately 4 for a change in applied direct‐current electric field of ∼140 kV/cm. Ultrafast nonlinear refraction causing phase changes of over π radians without appreciable excess loss is observed. These measurements demonstrate that GaAs/AlGaAs MQW waveguides could be successfully used for subpicosecond all‐optical switching near half‐band gap, at wavelengths corresponding to the 1.55 μm optical communications band.

We report the structure and lasing characteristics of GaAs/AlGaAs vertically stacked multiple‐quantum‐wire (QWR) semiconductor lasers grown by organometallic chemical vapor deposition on V‐grooved substrates. The active region in these lasers consists of three crescent‐shaped wires, placed at the center of a single‐mode optical waveguide. The higher optical confinement factor, compared to single‐QWR structures, leads to reduced threshold currents, as low as 0.6 mA for high‐reflection coated devices at room temperature. The lower threshold carrier density results in oscillation at a lower QWR subband as compared to single‐QWR laser structures.

Selective area growth (etching) by low‐pressure organometallic chemical vapor deposition (LP‐OMCVD) is utilized to intentionally modulate the local growth (etch) rate by choosing the pattern of dielectric‐masked areas, thereby defining III‐V semiconductor structures in situ. This technique is applied to tune the emission wavelength of a GaAs/AlGaAs quantum well structure, and to obtain InP/InGaAs superlattice structures tapered in thickness with growth rate increases as high as 800%, suitable for integrated optics applications. In contrast, selective deposition by organometallic molecular beam epitaxy (OMMBE) does not produce growth rate enhancements, thereby preventing similar in situ definition schemes but allowing to integrate structures with optimized nominal thicknesses.

We demonstrate a novel waveguide structure for realization of integrated optics with compact waveguide bends (radii≊1 mm), low propagation loss (0.45 dB/cm), and large guide dimensions (5 μm width) to facilitate input coupling. Experimental results using single‐mode GaAs/AlGaAs heterostructure guides at 1.52 μm wavelength are presented.

We report the study of organometallic chemical vapor deposition (OMCVD) on the stepped surfaces obtained by crystal growth on nonplanar vicinal (100) GaAs substrates. Scanning and transmission electron microscopy investigations were combined to identify two distinct diffusion mechanisms in OMCVD: one mechanism involves the gas phase and allows us to selectively distribute the incoming flux of volatile reactants between two adjacent facets; the other one involves surface diffusion of nonvolatile species over distances in the hundred nm range. Spectrally and spatially resolved cathodoluminescence imaging of the light emissions from a single quantum well structure gives direct evidence that the quantum well thickness variations, which can be controlled over a wide range (up to 1:5) by growth parameters, produce effective band‐gap variations.

We report on the growth of dense lateral arrays of GaAs quantum wire structures, obtained by organometallic chemical vapor deposition (OMCVD) on GaAs substrates where a submicron grating has been lithographically defined and etched prior to deposition. The experiments were performed simultaneously on (100) oriented substrates, where the wires are virtually ‘‘isolated’’ from each other, and on substrates that are vicinal with respect to the (100) orientation, where the wires are ‘‘smoothly connected’’ by quantum wells. Transmission electron microscopy investigations allowed the study of the morphology of the resulting structures, which was related to the microscopic step nature of the starting surfaces and revealed important basic aspects of growth dynamics.

Single (SQW) and double (DQW) quantum well composite cavity GaAs/AlGaAs lasers with an integrated passive section were fabricated and compared. Si implantation was used for partial quantum well disordering in the passive section. Implanted DQW lasers with a 2.6‐mm‐long cavity had threshold currents of 26.3 mA compared to 33 mA for implanted SQW lasers. The measured resonant absorption in the passive section showed an exponential roll‐off in agreement with Urbach’s law. The characteristic energy E0 associated with Urbach’s law was 6 meV for untreated SQW and DQW lasers and ≊11 meV for implanted SQW and DQW lasers.

Photoluminescence, electroluminescence, and current measurements are used to probe the internal field in an n+‐n‐n+ GaAs/AlGaAs superlattice. At low bias voltages, the photoluminescence spectrum shows several peaks arising from electric field domains in the superlattice. Their positions correlate with features in the current‐voltage characteristic and are consistent with a simple calculation of the Stark shift. Above the threshold voltage for impact ionization we observe spectrally narrow electroluminescence (width 3.5 meV). The energy of this emission coincides with the zero‐field photoluminescence signal, indicating that electrons and holes screen the applied electric field in the quantum wells.

We report measurements of the two‐photon absorption coefficient of GaAs optical waveguide structures at 1.06 μm. We show that for pulse lengths longer than ∼1 ps, light‐induced index changes sufficient to induce all‐optical switching will be predominantly due to carriers generated by two‐photon absorption. These results allow us to predict limitations for ultrafast all‐optical GaAs devices.

Rib waveguides have been fabricated without any post‐crystal growth processing steps. The ribs are defined by the two nongrowth (111)B surfaces that develop at each edge of (011) mesas on a patterned GaAs substrate during organometallic chemical vapor deposition (OMCVD) of GaAs/AlGaAs structures. Propagation losses as low as 0.6 dB/cm at 1.52 μm wavelength have been obtained, which is attributed to the smoothness of the (111)B facets defining the GaAs guiding layer. This study revealed the importance of surface diffusion‐enhanced crystal growth when a growth surface is adjacent to a nongrowth surface such as a (111)B facet. This effect was quantified here and its magnitude suggests that the OMCVD technique would be well suited for the growth of structures tapered in three dimensions, of interest for integrated optics applications.

A modulation‐doped junction field‐effect transistor incorporating an optical waveguide under the gate modulates light by the carrier band‐filling effect (two‐dimensional Moss–Burstein effect) in a single quantum well, achieving a 5:1 extinction ratio in a 250‐μm‐long waveguide for 4 V reverse gate‐source bias Vgs swing and 0 V drain‐source bias Vds. Similar performance is obtained over a 16 nm spectral range. A novel band‐edge transparency effect is observed for Vds>0 allowing an extinction ratio of 10:1, corresponding to a change in absorption of 92 cm−1 to be obtained through band‐gap dilation by hot electrons at biases of Vds =8 V. Below‐band‐gap refractive index modulation of 1.6×10−3 is obtained for a Vgs swing of 2.4 V. The novel junction field‐effect transistor optical modulator also functions as a photovoltaic or photoconductive optical detector, a transistor, and a light‐emitting diode.

We describe tunneling measurements of the electronic states of superlattices in which an electric field has destroyed the miniband structure. The tunneling characteristics reveal that the minibands collapse into localized Wannier–Stark states, which can be resolved in the first two quantum wells of the superlattice. The positions can be accounted for quantitatively by a combination of electrostatic and quantum mechanical effects.

Integrated external cavity GaAs/AlGaAs single quantum well lasers were fabricated by selective quantum well disordering. Lasers with 2.07‐mm‐long passive sections and 0.48‐mm‐long active sections had threshold currents of 33 mA, compared to 9.8 mA for lasers without passive sections. Lasing data indicate a residual modal loss of 11 cm−1 in the passive sections, consistent with direct waveguide loss measurements. Control composite structures with a nondisordered quantum well in the passive sections showed significantly higher threshold currents and a large red shift of as much as 11.4 nm in the lasing wavelength compared to lasers without a passive cavity. This red shift is the main reason for the reduced resonant losses in integrated external cavity lasers with a nondisordered quantum well in the passive section.

Device quality GaAs was grown in a conventional organometallic chemical vapor deposition reactor, using sequential group III (trimethylgallium, TMG) and group V (arsine) reactant gas exposures typical of atomic layer epitaxy (ALE). The results show that, at a given temperature, impurity (e.g., carbon) incorporation is controlled by the effective V/III ratio at the growing surface, which is determined by the sequence used in the growth cycles. This effect, specific to ALE, is quantified by solving the diffusion equation that describes concentration transients at the growing surface. Detailed photoluminescence experiments identified C and Mg as the residual acceptors and Ge as the sole residual donor in a 3×1015 cm−3 n‐type background layer with mobilities of 5600 cm2/V s at room temperature and 35 000 cm2/V s at 77 K. A higher purity sample showed reduced levels of Ge, with traces of S, Si, and Te donors and only C acceptors.

We show that macroscopic, as opposed to microscopic, steps can be obtained on a semiconductor vicinal surface when a perturbation has been ‘‘printed’’ on it, prior to epitaxial growth. This generic crystal growth concept has been studied here with the GaAs/AlGaAs system using organometallic chemical vapor deposition. The details of step formation, stabilization, and subsequent propagation have been investigated with scanning electron microscopy. Regular, sawtooth‐like growth patterns have been obtained, with periodic growth rate differences at the step edges. This novel lateral patterning technique was employed to fabricate arrays of quantum wire‐like heterostructures.

We demonstrate how an adequate choice of growth conditions and GaAs/AlGaAs superlattice series leads to a desired refractive index profile and to confinement of light at the cusp of a planarized structure over a previously photolithographically etched groove. Waveguiding at 1.52 μm wavelength with measured propagation losses of 1.5 dB/cm was obtained in these structures. The effect of growth parameters is discussed and potential applications of this concept to other structures suitable for guided‐wave devices are proposed.

We present TE and TM waveguide loss measurements of partially disordered GaAs/AlGaAs quantum well separate confinement laser structures. Disordering is accomplished by silicon ion implanation and subsequent annealing. Propagation losses as low as 9 cm−1 are observed at the lasing wavelength of the corresponding untreated laser wafer. The waveguides are shown to be compatible with fabrication and dimensional requirements of high quality semiconductor lasers; ridge waveguide lasers fabricated in unimplanted portions of the same wafer exhibit threshold currents of only 8 mA. The results show that impurity‐induced quantum well disordering is suitable for monolithic integration of low‐threshold quantum well lasers and transparent optical waveguides.