C. A. Armiento

Gigabit transmitter array modules on silicon waferboard

Individually addressable, four-channel transmitter arrays operating at data rates of 1 Gb/s have been developed based on a hybrid optoelectronic integration approach called silicon waferboard. A key feature of silicon waferboard is the use of mechanical alignment features fabricated on the surface of a silicon chip that enable passive optical alignment of components such as lasers and optical fibers. The transmitter array, which operates at a wavelength of 1.3 mu m, comprises a four-channel InGaAsP/InP laser array that is passively aligned to four single-mode fibers held in V-grooves. The transmitter array also includes a four-channel GaAs MESFET driver array chip that provides high-speed drive currents to the individual lasers. The laser array, driver array, and optical fibers are all spaced on 350- mu m centers, which results in a four-channel transmitter array that fits within a width of only 2 mm. Transmitter array waferboards were housed in a specially developed package to permit high-frequency characterization. These transmitter array modules have demonstrated operation at data rates of 1 Gb/s per channel, with an interchannel crosstalk of -29 dB. >

GaAs/AlGaAs quantum‐well intermixing using shallow ion implantation and rapid thermal annealing

Low‐energy As+‐ion implantation followed by rapid thermal annealing (RTA) was utilized to modify exciton transition energies of GaAs/AlGaAs quantum wells (QW). A variety of structures were irradiated at an energy low enough that the disordered region was spatially separated from the QWs. After RTA, exciton energies showed large increases which were dependent on QW widths and the implantation fluence with no significant increases in peak linewidths. The observed energy shifts were interpreted as resulting from the modification of the shapes of the as‐grown QWs due to enhanced Ga and Al interdiffusion at heterointerfaces in irradiated areas. These results are consistent with the model of enhanced intermixing of Al and Ga atoms in depth of the material due to diffusion of vacancies generated near the surface.

Impact ionization in (100), (110), and (111) oriented InP avalanche photodiodes

The impact ionization process in the 〈100〉, 〈110〉, and 〈111〉 crystallographic directions in InP has been investigated by analysis of photomultiplication and multiplication noise data from InP avalanche photodiodes. This is the first report of such measurements for (110)‐oriented InP and the first consistent investigation of impact ionization in the three principal crystallographic directions. Our measurements indicate that, unlike the reports for GaAs, no significant orientation dependence of the impact ionization coefficients exists in InP. Momentum‐randomizing collisions with phonons, which result in intervalley transfer of energetic electrons, are believed to be the reason for the lack of anisotropy in the electron impact ionization coefficients.

Ionization coefficients of electrons and holes in InP

The ionization coefficients of electrons and holes in InP have been determined from photomultiplication measurements on abrupt‐junction low‐leakage np+ InP avalanche photodiodes. The ionization rate of holes ( β) was found to be greater than that for electrons (α), the ratio varying with peak electric field Em from β/α=3.8 at Em=4.85×105 V cm−1 to β/α=2.7 at Em=6.37×105 V cm−1.

Quantum well shape modification using vacancy generation and rapid thermal annealing

The effect of rapid thermal annealing (RTA) on the shapes of GaAs/AlGaAs quantum wells (QWs) has been investigated by monitoring exciton energies using low temperature photoluminescence and photoluminescence excitation spectroscopies. After RTA, large changes in exciton energies were observed only in regions of the samples in which excess surface vacancies were generated, either by capping with a thin layer of SiO2 or by low-energy ion implantation. These changes were interpreted as resulting from modifications of the shapes of the as-grown QWs from abrupt or square to gradual (rounded) due to enhanced interdiffusion of well/barrier atoms. For single QWs there was an increase in exciton energy whose magnitude depended on the width of the well, its distance from the surface of the wafer, the annealing temperature and the total number of surface vacancies available. From studies of coupled QWs, there was clear evidence of asymmetry in the heterostructure after RTA. Although both techniques of vacancy generation yield substantial QW shape modifications, the ion implantation technique has the advantages of being highly reproducible and of being compatible with any material system.

Beryllium‐ion implantation in InP and In1−xGaxAsyP1−y

Anneal temperatures ⩾700 °C are necessary to obtain maximum electrical activation of implanted Be in InP. At these temperatures, activation ≳50% is generally achievable. Both the implant temperature and implanted‐Be concentration affect p‐n junction depth and presumably, therefore, the in‐diffusion of implanted Be. For room‐temperature implants, the maximum Be concentration which showed insignificant in‐diffusion was 3×1018 cm−3. Using a multienergy implant schedule (highest energy 400 keV), which results in a flat as‐implanted Be concentration of ≈3×1018 cm−3, sheet hole concentrations as high as 2.2×1014 and 1.5×1014 cm−2 have been obtained in InP and In0.75Ga0.25As0.52P0.48, respectively.Anneal temperatures > or =700 /sup 0/C are necessary to obtain maximum electrical activation of implanted Be in InP. At these temperatures, activation >50% is generally achievable. Both the implant temperature and implanted-Be concentration affect p-n junction depth and presumably, therefore, the in-diffusion of implanted Be. For room-temperature implants, the maximum Be concentration which showed insignificant in-diffusion was 3 x 10/sup 18/ cm/sup -3/. Using a multienergy implant schedule (highest energy 400 keV), which results in a flat as-implanted Be concentration of approx. =3 x 10/sup 18/ cm/sup -3/, sheet hole concentrations as high as 2.2 x 10/sup 14/ and 1.5 x 10/sup 14/ cm/sup -2/ have been obtained in InP and In/sub 0.75/Ga/sub 0.25/As/sub 0.52/P/sub 0.48/, respectively.

Effect of heat treatment on InGaAs/GaAs quantum wells

We report on the effect of furnace annealing on 60‐A‐wide InxGa1−xAs/GaAs single quantum wells (SQWs) in the range of indium composition 0.1≤x≤0.5. Excitonic energy shifts of up to 120 meV were observed after annealing of the samples at 825 °C for 30 min. The fact that these energy shifts were strongly dependent of the indium composition in the well material was consistent with enhancement on the indium diffusion out of the wells associated with the presence of dislocations. The most dramatic changes, as a result of annealing, manifested by strain recovery were observed from the SQW with x=0.3 which as‐grown had a low dislocation density (quantum well thickness slightly exceeding the critical layer thickness for formation of dislocations).

Improved activation of Mg+ and As+ dual implants in GaAs by capless rapid thermal annealing

The activation of high dose Mg+ implants (1×1015 cm−2, 100 keV) in GaAs using capless rapid thermal annealing has been improved by the co‐implantation of As+. This technique reduces the outdiffusion of the implanted Mg, which can adversely affect the activation of shallow, high dose implants. Compared with an activation of 18% for an implant of Mg+ only, the co‐implantation of As+ has increased the activation to as much as 61% with concomitant sheet resistance of 136 Ω/⧠. The placement of the As+ implant with respect to the position of the Mg+ profile has been determined to play a role in the activation efficiency. This technique has been applied to the formation of thick p+ regions with high surface carrier concentrations, which has important applications in device fabrication for reduction of contact resistances.

Diffusion length of moles in n‐InP

By measuring the photocurrent as a function of reverse bias for InP photodiodes with a range of junction depths, the hole diffusion length Lp of epitaxial n‐type InP (n∼1.5×1016 cm−3) was determined to be approximately 12 μm. This value of Lp is an order of magnitude larger than that determined by the electron beam induced current and surface photovoltage techniques. Reasons for these discrepancies, which involve geometrical and material considerations, respectively, are discussed.

Monolithically integrated laser/rear-facet monitor arrays with V-groove for passive optical fiber alignment

An InGaAsP/InP laser monolithically integrated with a rear facet monitor and a fiber V-groove has been demonstrated for the first time. The integrated device incorporates an etched-facet laser fabricated using an in situ, multistep, reactive ion etch process. The integrated V-groove, which is etched directly into the InP substrate, is designed to enable passive alignment of an optical fiber to the active region of the laser. Passive coupling efficiencies of 18% and 8% have been obtained using cleaved multimode and single mode fibers, respectively. Responsivities of the rear facet monitor were as high as 0.49 A/W.<<ETX>>