On-area wire bonding of HgCdTe photoconductive (PC) infrared detectors usually causes material damage underneath the bonding pads. Such damage may propagate into the active area, potentially degrading performance and posing long-term reliability problems. Some off-area bonding fabrication techniques can also induce some degree of semiconductor material damage. In this paper, we report a relatively straightforward off-area bonding scheme that solves these problems. The process uses multiple photolithography and chemical etching steps to create a continuous slope or staircase in the HgCdTe leading down to the epoxy surface. The staircase ensures smooth step coverage for the subsequent metalization. Tri-layer photolithography (resist /metal/resist) and reactive ion etching (RIE) is then used to remove the epoxy in the bonding pad area. Since all areas other than the pad region are protected by the metal film, no RIE radiation damage is induced to the active area. The contact metalization is achieved by using standard liftoff techniques. Our so called staircase off-area bonding fabrication technique can be used to fabricate highly reliable, high density, small-size, detector arrays.

The inelastic light scattering spectra of chalcopyrite structure ZnGeP2 crystals grown by an improved low temperature crystallization from the nonstoichiometric solution of this compound in the liquid Bi or liquid Tl solutions as well as grown by high temperature Bridgman technique has been investigated together with the optical absorption and electron transport measurements.

ZnGeP2 crystallized from the melt via horizontal gradient freezing shows the tendency to decompose into Ge and GeP when the equilibrium vapor pressure is not exactly controlled during the entire crystallization process. Using differential thermal analysis (DTA) it was found that ZnGeP2 has a truly congruent melting point of 1311 K. Adding small amounts of the elements and binaries in the ternary system Zn-Ge-P to stoichiometric ZnGeP2 a significant deflection of the liquidus curve was observed at the melting point of ZnGeP2- From DTA, X-ray diffractometry (XRD), photoluminescence (PL), transmission and conductivity measurements it was concluded that the melt grown material was highly compensated. The presence of a broad acceptor and donor band in the band gap could be associated with phosphorous and zinc point defects in the crystal lattice. It is assumed that the defect concentrations are of the order 1019 cm−3.

ZnGeP2 can be transported by chemical vapor transport (CVT) using phosphorus or ZnP2 as transporting agent. Since germanium has a seven order of magnitude smaller partial pressure than zinc and phosphorus solely the formation of a volatile GePy (y≥l) species can explain the CVT-growth which was observed in a temperature range from 973 to 1573 K. To stabilize this species phosphorus pressures in the bar range are needed. Using absorption spectroscopy to analyze the equilibrium vapor phase composition over P, GeP and ZnGeP2, absorption lines were found adjacent to P2 band heads in the wavelength range from 180 to 260 nm which were addressed as band heads of an unknown GePy species. Quadrupole mass spectroscopy (QMS) measurements revealed that this species is not stable at lower pressures decomposing presynthesized GeP and ZnGeP2 in a Knudsen cell. In the temperature range from 550 to 800 K at total pressures of 10−7 to 10−6 mbar, ZnGeP2 decomposes into Zn and P4 whereas Zn is the dominant gas phase species. Under vacuum ZnGeP2 starts to decompose at 600 K while in a N2 atmosphere decomposition occurs at 923 K. By adding ZnP2 (5mg/cm3) to polycrystalline ZnGeP2, which was placed in an evacuated and closed quartz glass ampoule, red transparent crystals were yielded in a temperature gradient ΔT= 1073–1023 K.

Electron paramagnetic resonance (EPR) has been used to monitor native defects, both acceptors and donors, in ZnGeP2 crystals grown by the horizontal gradient freeze technique. These active centers include singly ionized zinc vacancies (Vzn-), neutral phosphorus vacancies (VP0), and neutral phosphorus antisite defects (PGe0). The concentration of Vzn− acceptors correlates with the near-infrared optical absorption present in all ZnGeP2 crystals. A photoluminescence band near 1.4 eV is shown to be polarized and is attributed to donor-acceptor-pair (DAP) recombination. Preliminary time-decay measurements support this assignment. Observation of the EPR spectrum of Mn2+ is also reported.

Steady state and time-resolved photoluminescence (PL) investigations on ZnGeP2 crystals grown from the vapor phase by high pressure physical vapor transport (HPVT) and from the melt by gradient freezing (GF) are reported. The luminescence spectra reveal a broad infrared emission with peak position at 1.2 eV that exhibits features of classical donor-acceptor recombination. The hyperbolic decay characteristic over a wide energy range, investigated from 1.2 eV up to 1.5eV, suggest that this broad emission band is related to one energetic recombination center. Higher energetic luminescence structures at 1.6eV and 1.7eV were revealed after annealing of ZnGeP2 crystals in vacuum for a longer period of time. The emission decay behavior in this energy range is characterized by two hyperbolic time constants, viewed as the supercomposition of the decay from the broad emission center peaked at 1.2eV and additional donor-acceptor recombination emissions at 1.6eV and 1.7eV, respectively. ZnGeP2 crystals grown under Ge-deficient conditions by HPVT show an additional emission structure at 1.8 eV with sharp emission fine structures at 1.778 eV related to the presence of additional donor states.

Photoluminescence (PL) steady-state spectra of p-ZnGeP2 (ZGP) single crystals grown by high- and low-temperature directed crystallization have been investigated. It is determined that the long-wavelength component PL with a maximum in the interval 1.2–1.5 eV for different crystals quenched in the temperature range 77–300 K. The long-wavelength component PL are due to donor-acceptor pair transitions. At room temperature the short-wavelength PL with a maximum near 1.85 eV becomes the determining component. The nature of this band discussed. The use of low-temperature directed crystallization reduces the concentration of lattice defects in ZGP single crystals and opens up the new possibilities for increasing the conversion efficiencies of nonlinear devices.

We demonstrate self-trapping of a two-dimensional beam at 1.3 microns wavelength in resonantly-enhanced InP. The self-trapped beam also induces a two-dimensional optical waveguide in bulk InP, which guides a second beam at 1.55 micron wavelength.

The Diffused Quantum Well (DFQW) structures created by both impurity induced and impurity free or vacancy promoted processes have recently been advanced to a higher level. The interdiffusion mechanism is no longer confined to two constituent atoms, but consists of two or multiple phase interdiffusion as well as multiple species, such as three cations interdiffusion and two pairs of cation-anion interdiffusion. Results show that the outcome of these interdiffusions is quite different. For instance, both compressive or tensile strain materials and both blue or red shifts in the bandgap can be achieved dependent on the type of interdiffusion. The advantage of being able to tune the material properties allows the realizations of higher performance lasers and modulators. Two lasing wavelengths (60 nm apart) are produced at λ ∼ 1.55μm, on the same substrate, with threshold currents of 290mA, and an extremely large relative reflectance change (over 10000) is predicted with power consumption reduced by 67%. A six fold enhancement of the third order susceptibility over that of the bulk materials can be achieved by using the inter-subband transitions in the DFQW at λ ∼ μm. Broadband (1000nm) detectors have also been realized due to the wide DFQW spectral bandwidth. Several state-of-the-art results of the DFQW will be summarized with an emphasis on the future developments and directions of the DFQW.

Compositional interdiffusion in Al0.3Ga0.7As/GaAs superlattice structures with equal 3.5 nm barrier and well widths induced by Si focused ion beam implantation and subsequent rapid thermal annealing has been modeled. A strong depth dependence of the mixing process is observed at a Si++ energy of 100 keV and at a dose of 1×1014 cm−2; this depth dependence is modeled by considering the second derivative of the vacancy profile. That is the maximum in the vacancy injection generated by the transient vacancy concentration gradient. We have included the dynamics of the spatial vacancy profile in the model and find good agreement with experimental results.

Interdiffusion across the well/barrier interfaces modifies the subband structure in AlGaAs/GaAs single quantum well (QW) structures. We have investigated the interrelated changes in both confinement energy of the subband states and the composition dependence of the bandgap energy in the QW, both of which are a strong function of the initial well width. Higher order transitions are found to be more sensitive than the ground state transitions to interdiffusion especially during the early stages of interdiffusion. These calculations model the experimental measurements (photoluminescence and photoreflectance) which are used to characterize interdiffused QW structures.

Theoretical results are presented showing how quantum well disordering affects the TE and TM absorption coefficient spectra of In0.53Ga0.47As/InP single quantum wells. An error function distribution is used to model the constituent atom composition after interdiffusion. Different interdiffusion rates on the group V and group III sublattices are considered resulting in a strained structure. With a suitable interdiffusion process the heavy hole and light hole ground state, excitonic transition energies merge and the absorption coefficient spectra near the fundamental absorption edge become polarization insensitive. The results also show that this polarization insensitivity can persist with the application of an electric field, which is of considerable interest in waveguide modulators.

Multiple cations interdiffusion in In0.53Ga0.47As/In0.52Al0.48As quantum well (QW) structure is investigated by using the model of expanded form of Fick's second law. The model is fitted to the measured concentration data in order to determine their diffusion coefficients. Once the concentration distribution is obtained, the types of strain and their variation across the QW can be determined, thus the subbands and transitions can be gathered. Result shows interesting phenomena due to this three species interdiffusion.

Optical waveguide type phase modulators defined by impurities induced disordering (IID) are investigated. To achieve a better optical confinement, a two steps ion implantation process is carried out to introduce additional impurities with respect to depth in the cladding region. A more uniform refractive index profile in deeper lateral confined region is obtained after thermal annealing. The refractive index different between the core and cladding can be adjusted by controlling the extension of interdiffusion in the cladding. This provide tuning of single mode operating region. For present IID phase modulator with 25 period of 100Å/100Å Al0.3Ga0.7As/GaAs multiple quantum wells single mode operating at 0.88//m, a normalized phase shift of 362°/Vmm. chirping parameter of 47, and absorption loss less than 120cm−1 are achieved theoretically.

The optical properties of In0.53Ga0.47As/InP single quantum well (QW) (with an as-grown well width of 60Å structures) interdiffused with different cation and anion interdiffusion rates have been theoretically analyzed for applications in optoelectronics. The interdiffusion of TnGaAs/InP QW structures is complicated as interdifrusion can occur for either (i) only group-Ill (In,Ga), (ii) group-V (As,P), or (iii) both group-Ill and group-V sublattices. Depending on the resulting composition profiles, the shifts (blue or red) of the transition energies can be tuned to wavelengths between 1.3μm to 1.55μm for device applications. The results show that the control of the rates of cation and anion interdiffusion offers interesting possibilities for designing optoelectronic devices such as modulators and lasers.

We will present results for an Al0.24Ga0.76As/GaAs diffused multiple quantum well with five periods of 100/100 Å thick well/barrier layers grown in between Al0.24Ga0.76As guiding layers and cladded on top by a 1 μm thick p-Al0.44Ga0.56As layer and on the bottom by an n-Al0.44Ga0.56As layer of equal thickness, on a n+-GaAs buffer layer and n+-GaAs substrate. Vacancy enhanced QW diffusion is employed where a 2000 Å thick layer of SiO2 is deposited on top of the diffused multiple quantum well structure. Photoluminescence measurement and photovoltage measurement at room temperature show that after rapid thermal annealing for 30 sec at 1000 °C to 1040 °C, a bandgap shift of 30 nm is obtained for the exciton edge. Further, this technique is applied to a ridge waveguide laser structure to make two windows for high power output up to 36 mW. This device shows that the diffusion process may have practical applications.

We describe a method of silicon oxide capped disordering of GaAs /AlGaAs multiple quantum wells (MQW) and its application to the fabrication of passive waveguides integrated with nonlinear switching sections. The silicon oxide cap in this work was formed by spinning a solution of glass forming compound and curing it. The characteristics of the disordering process has been studied by monitoring the shift of the photoluminescence as a function of rapid thermal annealing temperature and fitting the n=1 electron heavy-hole level to that calculated from an error function diffusion profile. Our results indicate a Ga-Al inter-diffusion constant of 8×10−16 cm2s−1 at 980°C and an activation energy of 4.4eV which is similar to values reported by other researchers.

The disordering process is then used to define selected areas of disordered and non-disordered MQWs and ridge waveguide structures were fabricated by conventional photolithography and wet chemical etching. Two structures have been studied. One is the nonlinear zero-gap directional coupler with disordered input and output branching waveguides, and the other is the symmetric nonlinear integrated Mach-Zehnder interferometer with one arm containing a non-intermixed MQW section. The devices investigated using a pump-probe set-up, exhibited strong all-optical switching behavior with a contrast ratio of 15:1.

The subject of this work is the simulation of Be diffusion during post-growth Rapid Thermal Annealing (RTA) of InGaAs epitaxial layers grown by Chemical Beam Epitaxy (CBE). This diffusion may occur during thermal treatments of InGaAs/InP Heterojunction Bipolar Transistors (HBT's), which contributes to limit the frequency performances of these devices. In order to characterize the Be depth profiles, Secondary Ion Mass Spectrometry (SIMS) has been used. The concentration dependent diffusivity has been covered to perform an improved data fitting of Be diffusion profiles. In a first step, the solid state diffusion mechanisms have been developed, including the Substitutional-Interstitial Diffusion (SID) and, in particular, Kick-out mechanism. To explain the observed concentration profiles and related diffusion mechanisms, a Generalized Substitutional-Interstitial Diffusion model is proposed. A simultaneous diffusion by Dissociative and Kick-out mechanisms is suggested. Good agreements between experimental depth profiles and simulated curves have been obtained.

An essentially impurity free, direct write and potentially high spatial resolution quantum well intermixing technique using pulsed laser irradiation is reported. This technique uses a Q-switched Nd:YAG laser emitting at 1.06 μm with a pulse length of ∼20 ns and repetition rate of 10 Hz. The typical energy densities used for both Gain As/Gain AsP and GaAs/AlGaAs structures were ∼ 5 mJ mm−2. Multiphoton interactions with carriers lead to phonon emission, the phonons interact with the lattice thus generating point defects which diffuse during a subsequent annealing stage in a rapid thermal annealer and cause intermixing. Photoluminescence measurements have demonstrated that the spatial resolution of the process is better than the resolution of the PL measurement (ie better than 25 μm) and the technique has been used to write directly a grating of period 1.25 μm into a GalnAs/GalnAsP quantum well structure. This was achieved using a grating of period 2.5 μm etched into the surface of the substrate; when illuminated by the Q-switched pulses this grating generated a volume hologram of point defects within the sample at half the etched period. A clear dip in the transmission spectrum of the waveguide which had been processed in this way was observed at 1.525 μm. Differential bandgap shifts of up to 40 meV have been observed in GaAs/AlGaAs double quantum well samples. 3 μm wide ridge waveguide lasers were fabricated from the intermixed and control samples. The threshold currents of the intermixed and the control lasers were comparable. The slope efficiency of the intermixed lasers showed insignificant changes when compared to the as-grown lasers.

A spatially selective quantum well intermixing process, using phosphorus-doped silica (SiO2:P) containing 5 wt% P to inhibit intermixing and pure SiO2 to enhance intermixing, is presented. The SiO2:P cap has been found to suppress bandgap shifts in both p-i-n and n-i-p GaAs/AlGaAs quantum well laser structures, with bandgap shift differences as large as 100 meV observed from samples capped with SiO2 and with SiO2:P after rapid thermal processing at temperatures as high as 950 °C for 60 s. Extended cavity ridge lasers exhibited low threshold currents with TE losses of 3.2 cm−1 measured in the passive waveguide sections at the lasing wavelength using the Fabry-Perot resonance method. This value is among the lowest reported so far using an impurity-free disordering technique.

Interband transitions of a series of as-grown AlGaAs/GaAs quantum well structures grown by MOVPE have been studied using photoreflectance to determine their well shape. The transition energies calculated using three different quantum well profiles are compared to those obtained using photoreflectance. The results show that the shape of these structures is best represented by an exponential potential profile.