I. V. Mitchell

Defect diffusion in ion implanted AlGaAs and InP: Consequences for quantum well intermixing

InGaAs/GaAs/AlGaAs and InGaAs/InGaAsP/InP laser structures, with InGaAs quantum wells approximately 1.85 μm beneath the surface, were implanted with ions having energies up to 8.6 MeV. Intermixing of the quantum wells, after rapid thermal annealing, was monitored through changes in the energy, linewidth, and intensity of the photoluminescence peak from the quantum wells. Where the defects had to diffuse primarily through Al0.71Ga0.29As, these quantities correlate strongly, for short anneal times, with calculated vacancy generation and ion deposition at the depth of the quantum well prior to annealing. This suggests that the defect diffusion length in the AlGaAs and/or GaAs is quite low. For diffusion primarily through InP, the photoluminescence data correlated well with the calculated total number of vacancies created in the sample, suggesting that defect diffusion is very efficient in InP.

Enhanced degradation resistance of quantum dot lasers to radiation damage

We compare the degradation of InAs/GaAs quantum well (QW) and quantum dot (QD) laser diodes following irradiation by high energy (8.56 MeV) phosphorous ions. Over a fluence range of 108–1011 ions/cm2, the degradation of the low temperature QD photoluminescence and electroluminescence emission is greatly suppressed relative to that of QW based devices (×100 and ×1000, respectively at the highest dose studied). Irradiated QD laser diodes demonstrated lasing action over the entire range of fluences, and 2 orders of magnitude beyond the maximum dose sustainable by QW devices. The improved damage response of QD based structures results from efficient collection and localization of electrons and holes by QDs in the active region, which limit carrier transfer to nonradiative centers. This work suggests the suitability of QD device architectures for use in radiation environments, and in high power applications, wherever nonradiative processes promote the degradation or failure of traditional QW devices.

Band‐gap tuning of InGaAs/InGaAsP/InP laser using high energy ion implantation

The technique of ion‐induced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation has been used to tune the emission wavelength of an InGaAs/InGaAsP/InP multiple quantum well (MQW) laser operating at 1.5 μm. The optical quality of the band‐gap shifted material is assessed using low‐temperature photoluminescence (PL). The band‐gap tuned lasers are characterized in terms of threshold current density and external quantum efficiency and exhibit blue shifts in the lasing spectra of up to 63 nm. This approach offers the prospect of a powerful and relatively simple fabrication technique for integrating active as well as passive optoelectronic devices.

ENHANCED GROUP-V INTERMIXING IN INGAAS/INP QUANTUM WELLS STUDIED BY CROSS-SECTIONAL SCANNING TUNNELING MICROSCOPY

Cross-sectional scanning tunneling microscopy is used to study InGaAs/InP quantum-well intermixing produced by phosphorus implantation. When phosphorus ions are implanted in a cap layer in front of the quantum wells (in contrast to earlier work involving implantation through the wells), clear strain development is observed at the interfaces between quantum well and barrier layers after annealing. This is interpreted in terms of enhanced group-V compared to group-III interdiffusion.

Selective amorphization of ion‐bombarded SiGe strained‐layer superlattices

Si/SixGe1−x multilayers were implanted with Si ions of 540 keV at doses between 1.0×1014 and 2.5×1015 ions/cm2. Channeling spectra were taken using 3 MeV B++ ions. These measurements showed a rapid increase of the Ge minimum yield with implantation dose. The increases were paralleled by a growth of disorder peaks in those parts of the Si backscattering spectrum corresponding to the SixGe1−x layers. After 1.2×1015 Si ions/cm2 the SiGe layers were completely amorphized. Cross‐sectional transmission electron microscope pictures confirmed the selective amorphization of the SiGe layers. Annealing of an irradiated sample resulted in recrystallization of all the amorphous layers in the 450–550 °C temperature range.

Nitrogen content of oxynitride films on Si(100)

The absolute nitrogen concentration in SiOxNy/Si films grown by rapid thermal oxidation in N2O has been determined by nuclear reaction analysis. Compared with conventional surface analysis methods, i.e., Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and secondary ion mass spectrometry, the nuclear reaction 14N(d,α)12C provides more accurate depth profiles of 14N due to the quantitative nature of the technique and its high sensitivity, ∼6.0×1013 atoms cm2. Silicon oxynitride films prepared under various conditions, specifically different growing temperatures and times, were analyzed. Nitrogen is observed to accumulate in a narrow region in the oxynitride (within ≲2.5 nm) close to the interface; the total amount of nitrogen increases with increasing temperature and growth time.

Argon incorporation in Si(100) by ion bombardment at 15–100 eV

Argon incorporation in Si(100) by low energy ion bombardment has been studied by polar angle dependent x‐ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The bombardment was performed at 15, 20, and 100 eV in an ultrahigh vacuum chamber where a mass‐separated argon ion beam with an energy spread of less than 1 eV was directed to the target. Both the argon penetration depth and incorporation probability were found to increase with bombardment energy. With a fluence of 2×1017/cm2, most of the incorporated argon was located within 20 A of the target surface for the 100 eV bombardment and within 10 A for the 15 eV bombardment. In all cases, the argon depth distribution reached a maximum and then declined. At this fluence, the incorporation probabilities were 0.0015 and 0.0004 for the 100 and 15 eV bombardment, respectively. When the amount of incorporated argon was measured as a function of fluence, it increased with fluence at low fluences, reached a quasisaturation at about 1×1016/...

Polarization insensitive InGaAs/InGaAsP/InP amplifiers using quantum well intermixing

A polarization insensitive optical amplifier based on a lattice matched InGaAs/InGaAsP/InP multiple quantum well (MQW) laser structure operating at 1.5 μm has been fabricated through vacancy enhanced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation. A simple model shows that if the interdiffusion rate of the anions is larger than that of the cations, the blue shift in the ground state heavy hole transition energy after implantation and annealing is greater than the light hole state blue shift, bringing the two bands together. Current–voltage measurements indicate that junction characteristics are well maintained after implantation. This simple technique for fabricating polarization insensitive optical amplifiers is readily extended to the monolithical integration of such devices along with other passive and active optoelectronic devices and opens the door to practical photonic integrated circuits.

A structural study of PdCu(100) surface alloys

Abstract The structures formed by one-half and one monolayer (ML) of Pd evaporated onto Cu(100) at 300 K were studied by low energy electron diffraction (LEED), medium energy ion scattering (MEIS), thermal desorption spectroscopy (TDS), and embedded atom method (EAM) calculations. In the half monolayer case, the LEED I(E) curves are consistent with the established c(2 × 2) surface alloy model. The MEIS data, however, suggest that a fraction of the Pd ( ∼ 1 4 ) is in “second layer” sites, in agreement with previous LEIS, TDS and XPS forward scattering measurements. The EAM simulations support the formation of alloy islands, providing a mechanism for the covering of some Pd atoms. As the deposition proceeds, however, this island formation is indicated to occur preferentially over clean copper. In the one monolayer case, a p(2 × 2)-p4g LEED pattern is observed. Analysis of the I(E) curves suggests that this arises from (100) Pd packed above the c(2 × 2) alloy. EAM calculations confirm the stability of this model. Evidence from MEIS and TDS, however, shows that the one monolayer surface as prepared in this work is inhomogeneous. c(2 × 2) and Cu rich surface domains exist in addition to those having the p4g Pd c (2 × 2) PdCu structure.

InGaAs/InP quantum well intermixing studied by cross-sectional scanning tunneling microscopy

Cross-sectional scanning tunneling microscopy (STM) is used to study lattice matched InGaAs/InP quantum well (QW) intermixing induced by ion implantation and thermal annealing. Different strain development in QWs (determined by STM topography of elastic relaxation in cross sectionally cleaved samples) is found to be dependent upon the range of the implanted ions relative to the QWs. It is found that the quantum wells remain latticed matched to the barrier layers after intermixing when ions are implanted through the multiple quantum well (MQW) stack. A shallow implantation in which ions are implanted into the cap layer above the MQW stack leads to tensilely strained wells and compressively strained interfaces between wells and barriers. The strain development in the latter case is attributed to different degrees of interdiffusion on the group III and group V sublattices. Finite element elastic computations are used to extract the group V and group III interdiffusion length ratio, and results using differen...