Showing papers by "Evelyn L. Hu published in 1996"
TL;DR: In this paper, a low threshold laterally oxidised long wavelength (1.55 µm) vertical cavity laser was demonstrated and the first submilliamp threshold current (0.8 mA) was achieved.
Abstract: The authors demonstrate a low threshold laterally oxidised long wavelength (1.55 µm) vertical cavity laser. The devices exhibit the first submilliamp threshold current (0.8 mA) as well as the highest reported operating temperatures (64°C CW and 95°C pulsed) of any long wavelength vertical cavity laser.
80 citations
TL;DR: In this paper, the extent of relaxation and orientation of linearly graded InxAl1-xAs (x=0.05-0.25) buffers were examined using a novel x-ray diffraction reciprocal space mapping technique (kmap).
Abstract: The extent of relaxation and orientation of linearly graded InxAl1‐xAs (x=0.05–0.25) buffers grown on GaAs were examined using a novel x‐ray diffraction reciprocal‐space mapping technique (kmap). Samples were grown at temperatures ranging from 370 to 550 °C. The fractional relaxation of the buffers grown between 470 and 550 °C was essentially identical (77%) and symmetric in orthogonal 〈110〉 directions. These buffers are believed to be in equilibrium indicating that the incomplete relaxation is not a kinetic effect. The extent of relaxation was less than that expected for equilibrium relaxation in the absence of dislocation–dislocation interactions indicating that such interactions must be considered to accurately predict the extent of relaxation. The saturation of the relaxation as a function of temperature indicates that at the grading rate used (8% In/μm or 0.69% strain/μm), we are not working in a growth regime where the relaxation is nucleation limited. In addition, all the buffers are slightly tilte...
72 citations
Proceedings Article•
25 Feb 1996TL;DR: In this paper, the authors proposed a low-cost VCL source for optical communications at 1.3 and 1.55 µm wavelengths, and demonstrated that VCLs are potentially low cost sources for optical communication.
Abstract: Vertical-cavity lasers (VCLs) operating at 1.3 and 1.55 µm wavelengths are potentially low cost sources for optical communications.
48 citations
TL;DR: In this paper, the authors used a model that includes the effects of both channeling and defect diffusion and deduced a room-temperature diffusion constant of D∼1×10−15 cm2/s.
Abstract: There has been steady progress in understanding the propagation of low‐energy, ion‐induced damage into semiconductor substrates. The availability of specifically designed heterostructure substrates allows us to trace the profile of damage into the material. A number of experiments, together with theoretical simulations, have confirmed the important role played by fortuitous channeling of ions, deep into the material (e.g., >1000 A deep for incident ions energies ∼300 eV). Recent experiments have also shown the importance of rapid diffusion of ion‐created defects. Using a model that includes the effects of both channeling and defect diffusion, channeling and diffusion in ion damage (CHANDID), we have deduced a room‐temperature diffusion constant of D∼1×10−15 cm2/s. This is an extremely high value for diffusion at room temperature, and is more characteristic of diffusion taking place at temperatures of a few hundred to a few thousand degrees centigrade. One cause of this high value of D may be attributed to radiation enhanced diffusion: the creation of excess electrons and holes during the etch process whose subsequent nonradiative recombination transfers momentum to the defects. Preliminary experiments, which monitor the effects of above band‐gap illumination during ion bombardment, validate this picture. Such understanding, of intrinsic importance, can be used to design material and device structures in which the effects of ion damage may be mitigated.
40 citations
TL;DR: A length-dependent analysis of quantized conductance in split-gate constrictions fabricated on InAs/AlSb quantum-well heterostructures is presented, and the explanation is shown to be in agreement with recent theoretical analyses relating various scattering mechanisms to the breakdown of quantization conductance.
Abstract: A length-dependent analysis of quantized conductance in split-gate constrictions fabricated on InAs/AlSb quantum-well heterostructures is presented. Conductance steps with spacing within a few percent of 2 e/h are observed in constrictions with channel lengths of 0.2 mm. With increasing constriction length nearly ideal quantized conductance can still be observed, even in constrictions as long as 2.0 mm. The values of the quantized step heights are found to vary more from device to device with increasing length. Our lengthdependent data differ considerably from previous reports on GaAs/Al xGa12xAs split-gate devices where the quantized conductance was severely degraded for constriction lengths * 0.6 mm. Temperature-dependent measurements indicate that the 2.0mm-long devices have one-dimensional ~1D! subband spacings close to 10 meV. The improved length performance of our devices is believed to be due primarily to the increased 1D subband spacings relative to the magnitude of potential fluctuations in the channel region. Our explanation is shown to be in agreement with recent theoretical analyses relating various scattering mechanisms to the breakdown of quantized conductance. @S0163-1829 ~96!03719-8#
34 citations
TL;DR: In this paper, a novel long wavelength (1.55 μm) vertical cavity laser using a current constricting AlAs oxidation layer is reported, which exhibits record low room temperature continuous wave (cw) threshold current(1.3 mA) and highest cw operating temperature reported for long wavelength VCLs.
Abstract: We report a novel long wavelength(1.55 μm) vertical cavity laser using a current constricting AlAs oxidation layer. The devices exhibit record low room temperature continuous wave (cw) threshold current(1.3 mA) and highest cw operating temperature reported for long wavelength VCLs(39 °C). Wafer fusion is used to combined seven strain compensated InGaAsP wells between two Al(Ga)As/GaAs quarter wave mirrors.
33 citations
TL;DR: In this article, the influence of concurrent above-band-gap laser illumination on the damage profile of GaAs/AlGaAs heterostructures subject to low energy (sub-keV) ion bombardment was investigated.
Abstract: We have investigated the influence of concurrent above‐band‐gap laser illumination on the damage profile of GaAs/AlGaAs heterostructures subject to low energy (sub‐keV) Ar+ ion bombardment. A dramatic change in damage profile was observed for these samples, compared with those that were not laser illuminated, and the degradation increases with the illuminated power intensity. Below‐band‐gap illumination results in a minimal increase in damage profile. Such results indicate the possibility of radiation‐enhanced diffusion of defects, and may explain the observed high defect diffusivity at room temperature.
23 citations
TL;DR: In this paper, a GaAs MISFET with Al 2 O 3 formed by the wetoxidation of AlAs as the gate oxide is reported, and it is observed that hydrogenation treatment proves to be effective in reducing the state density at the GaAs interface due to removal of excess arsenic, which is a possible cause of interface states.
Abstract: A GaAs MISFET with Al 2 O 3 formed by the wet
oxidation of AlAs as the gate oxide is reported. It is observed that
hydrogenation treatment proves to be effective in reducing the state
density at the Al 2 O 3 /GaAs interface due to removal
of excess arsenic, which is a possible cause of interface states in this
system
22 citations
TL;DR: In this article, a Fabry-Perot technique was used to determine the reflectivity and phase of the interface between semiconductor and a multilayer metal structure as it will be realized in actual device fabrication.
Abstract: The authors describe a Fabry-Perot technique for determining the reflectivity and the phase of the interface between semiconductor and a multilayer metal structure as it will be realised in actual device fabrication. The reflection coefficients of GaAs to Ti/Au, Pd/Au, Au and Ag interfaces are measured at 1.55 /spl mu/m.
12 citations
13 Oct 1996
TL;DR: In this article, an improved laterally oxidized long wavelength (1.55/spl mu/m) InGaAsP vertical cavity DBR QW laser is presented.
Abstract: We demonstrate an improved laterally oxidized long wavelength (1.55-/spl mu/m) InGaAsP vertical cavity DBR QW laser. The devices exhibit the first submilliamp threshold current as well as the highest reported CW (64/spl deg/C) and pulsed (85/spl deg/C) operating temperatures.
11 citations
TL;DR: In this article, the authors have developed a simple technology for monolithic integration of resonant tunneling diodes (RTDs) and heterostructure junction-modulated field effect transistors (HJFETs).
Abstract: We have developed a simple technology for monolithic integration of resonant tunneling diodes (RTDs) and heterostructure junction-modulated field effect transistors (HJFETs). We have achieved good device performance with this technology: HJFETs had transconductances of 290 mS/mm and current densities of 310 mA/mm for a 1.5 μm gate length; RTDs had room temperature peak to valley ratios greater than 20:1 with current densities of 42 kA/cm2. With this technology, we have demonstrated a monolithically integrated RTD + HJFET state holding circuit that can serve as a building block circuit for self-timed logic units. This circuit is resistor-free and operates at room temperature. The state holding circuit showed large noise margins of 1.21 V and 0.71 V, respectively, for input low and input high, for a 1.7 V input voltage swing. We have examined the transient response of the circuit and investigated the effect of circuit design parameters on propagation delay. We identify the RTD valley current as the limiting factor on propagation delay. We discuss the suitability of RTD + HJFET circuits such as our state holding circuit for highly dense integrated circuits.
TL;DR: In this article, the fabrication process and characteristics of three consecutive runs of double-fused 1.5-μm vertical-cavity lasers are discussed, and the authors have measured light-current characteristics of over three hundred lasers with ten different diameters between 6 and 60 μm and observe a yield of over 95%.
Abstract: We discuss the fabrication process and characteristics of three consecutive runs of double-fused 1.5-μm vertical-cavity lasers. We have measured light-current characteristics of over three hundred lasers with ten different diameters between 6 and 60 μm and observe a yield of over 95%. The process and design improvements resulted in a low pulsed threshold current of 3 mA on a number of 6- and 8-μm-diameter devices and threshold current density of 2 kA cm−2 on 60-μm-diameter devices at room temperature.
21 Apr 1996
TL;DR: In this article, the authors demonstrated continuous-wave operation at room temperature using vertical-cavity lasers fabricated by two wafer fusion steps, which consisted of strain compensated InGaAsP quantum-well active layers sandwiched between two AlGaAs/GaAs quarterwave mirrors.
Abstract: The progress in understanding wafer-fused vertical-cavity lasers and improvements in fabrication techniques have led to the realization of the first room-temperature continuous-wave operating 1.54-/spl mu/m vertical-cavity lasers. By demonstrating continuous-wave operation at room temperature using vertical-cavity lasers fabricated by two wafer fusion steps, we have shown that wafer fusion is a viable technique. The lasers comprise strain compensated InGaAsP quantum-well active layers sandwiched between two AlGaAs/GaAs quarter-wave mirrors. Characteristics discussed include cavity losses, the gain-current density relationship, and voltage-current characteristics.
TL;DR: In this paper, a thin capping layer of annealed GaAs (∼210 A) grown at low temperature (LT•GaAs) can effectively block incident ions from penetrating into the growth substrate.
Abstract: A thin capping layer of annealed GaAs (∼210 A) grown at low temperature (LT‐GaAs) can effectively block incident ions from penetrating into the growth substrate. Ion‐bombarded, multiple quantum well structures capped by an annealed LT‐GaAs layer show a dramatic improvement in the photoluminescence, compared to samples capped with ‘‘normal’’ GaAs. The improvement appears to be correlated with the microstructures of the LT‐GaAs, since the improvement is particularly notable for samples annealed at 600 °C. This improvement in low energy ion‐induced damage is primarily the result of the reduced channeling of ions through the LT‐GaAs layer. These results suggest a potential application of LT‐GaAs in reducing ion damage and underscore the importance of the microstructure of arsenic precipitates in LT‐GaAs layers.
TL;DR: In this article, the first room-temperature continuous-wave (CW) 1.54 µm VCSEL was constructed by using a wafer-fused GaAs/AlGaAs mirror.
Abstract: Long-wavelength (1300/1550 nm) vertical-cavity surface-emitting lasers (VCSELs) have been much more difficult to realize than VCSELs at shorter wavelengths such as 850/980 nm. The primary reason for this has been the low refractive index difference and reflectivity associated with lattice-matched InP/InGaAsP mirrors. A solution to this problem is to “wafer-fuse” high-reflectivity GaAs/AlGaAs mirrors to InP/InGaAsP active regions. This process has led to the first room-temperature continuous-wave (CW) 1.54 µm VCSELs. In this paper, we discuss two device geometries which employ wafer-fused mirrors, both of which lead to CW operation. We also discuss fabrication of WDM arrays using long-wavelength VCSELs.
TL;DR: InAs-AlSb quantum wells contacted with periodic gratings of superconducting Nb electrodes show Josephson-junction characteristics at low temperatures, indicating the formation of a staggered vortex superlattice at twice the lithographic period.
Abstract: InAs-AlSb quantum wells contacted with periodic gratings of superconducting Nb electrodes show Josephson-junction characteristics at low temperatures. When a nonzero resistance is reestablished by a weak magnetic field, the resistance shows a strong component periodic in the magnetic field. At fields above \ensuremath{\sim}300 \ensuremath{\mu}T, the oscillation period corresponds to one flux quantum per grating cell; but in wide arrays (\ensuremath{\gtrsim}40 \ensuremath{\mu}m), a frequency doubling takes place at low fields, indicating the formation of a staggered vortex superlattice at twice the lithographic period.
TL;DR: In this article, the authors demonstrate a technique for providing lateral confinement by thermally desorbing portions of a GaAs quantum well using a monolayer AlAs mask, formed by depositing a fractional monolayers of AlAs in such a way as to form stable islands on the GaAs surface.
TL;DR: In this article, a low-energy, low-dose hydrogen ion treatment carried out at room temperature showed long-term improvement in the optical properties of near surface quantum wells, and applied this process to GaAs-based pseudomorphic HEMTs (PHEMTs) in order to improve their power performance.
Abstract: Surface passivation is a key issue in compound semiconductor device technology. The high density of surface states on unpassivated surfaces can lead to excessive non-radiative recombination at the surface, affecting optical devices, or provide leakage and low-field breakdown in electronic devices. Our previous studies on low energy, low-dose hydrogen ion treatment carried out at room temperature showed long-term improvement in the optical properties of near surface quantum wells. We have accordingly applied this process to GaAs-based pseudomorphic HEMTs (PHEMT) in order to improve their power performance. Although our process is designed so that the hydrogen reactions are confined to the surface of the substrate, a critical factor in the success of this treatment is the extent of in-diffusion of the hydrogen, and the possibility of dopant passivation. PHEMT structures were hydrogenated at various conditions and both Hall mobility and carrier density were monitored. For a low hydrogen ion dose (3 × 1016 cm−2) at 80 eV energy, some degradation of Hall mobility and carrier density was noted after the treatment, but full recovery of both parameters was achieved after a 400°C thermal anneal. Much higher hydrogen doses resulted in severe degradation of mobility and carrier density, which were only partially recovered after thermal anneal. Measurements on actual PHEMT devices showed an approximately 15% decrease in the transconductance, and in addition, a 60% decrease in the gate-to-drain leakage current after irradiation with 80 eV hydrogen ions at a dose of 3 × 1016 cm−2. The decrease of the leakage current indicates that passivation is taking place. The decrease of the transconductance suggests that hydrogen may be diffusing into the regions of the dopants. Optimization of the hydrogenation parameters should allow leakage reduction without sacrifice of transconductance.
TL;DR: In this article, a tunable soft x-ray synchrotron radiation source was used to study the chemical changes of oxidized GaAs and AlAs surfaces subject to exposure from hydrogen ions.
Abstract: We have performed photoemission experiments, using a tunable soft x‐ray synchrotron radiation source to study the chemical changes of oxidized GaAs and AlAs surfaces subject to exposure from hydrogen ions. Results indicate that the net effects for hydrogen ion irradiation are (i) the reduction of arsenic and (ii) the growth of the cation oxide components. The reduction of arsenic can result from the formation/desorption of arsine. The oxide overlayer after hydrogen ion treatments is dominated by cation oxides which are the more stable chemical species as described in the phase diagram. This oxide layer should then remain stable in atmosphere. These results can provide insight into the chemical reaction between hydrogen ions and oxidized AlGaAs surfaces.
TL;DR: In this article, a linear and circular Bragg-Fresnel Optics (BFO) was used in X-ray microdiffraction methods, in particular as applied to structural studies of complex fluids and biomaterials under confinement and flow conditions.
Abstract: We present results of simultaneous efforts to develop: 1.) Bragg-Fresnel Optics(BFO) to be used in X-ray microdiffraction methods, in particular as applied to structural studies of complex fluids and biomaterials under confinement and flow conditions; and 2.) Methodologies for confining complex fluids and biomaterials for in-situ structural studies. Using microelectronics process technology, we have fabricated linear and circular Bragg-Fresnel Lenses (BFL) in Si and III-V compound semiconductor substrates such as InP, GaAs and GaAs heterostructures with outermost zone width to 0.25 μm. X-ray characterization of linear BFLs were performed on a wiggler beamline at Stanford Synchrotron Radiation Laboratory (SSRL) at x-ray energies of 8 keV and 16 keV. A ∼5 μm focal spot size was obtained with a 50 μm incident beam, which was determined by the partial coherence of the source. On the confinement techniques, we have developed the X-ray Surface Force Apparatus (XSFA) which allows in-situ x-ray diffraction measurements to be made on fluid thin films confined between two atomically smooth surfaces. A new approach is being pursued to study the effects of confinement and flow on complex fluids and biological materials using microchannels fabricated on glass substrates.
13 Oct 1996
TL;DR: In this paper, an 818 nm strained Al/sub 0.15/In/sub sub 0.6/As multiquantum-well (MQW) was grown by solid source molecular beam epitaxy (MBE) with a threshold current density of 83 A/cm/sup 2/ per well.
Abstract: With post-growth rapid thermal annealing (RTA), 818 nm strained Al/sub 0.15/In/sub 0.25/Ga/sub 0.6/As multiquantum-well (MQW) lasers grown by solid source molecular beam epitaxy (MBE) showed a record low threshold current density of 83 A/cm/sup 2/ per well. Ridge waveguide lasers fabricated from the same material exhibited pulsed threshold current of 5 mA with 62% differential quantum efficiency.
TL;DR: In this article, the hydrogen was replaced with deuterium and confirmed that hydrogen is introduced into the substrate during methane/deuterium/argon reactive ion etching (RIE) with secondary ion mass spectrometry.
Abstract: In this work, we study the hydrogen introduced into InP during methane/hydrogen/argon reactive ion etching (RIE) to determine its effect on metalorganic chemical vapor deposition regrowth. We replace hydrogen with deuterium and confirm that deuterium is introduced into the substrate during methane/deuterium/argon RIE with secondary ion mass spectrometry. During regrowth, the deuterium diffuses from deep within the material and clusters at the regrowth interface, strongly indicating the presence of defects. To further understand the role of hydrogen, we investigate the separate effects of ion damage and hydrogenation on subsequent regrowth. We find that photoluminescence of regrown quantum wells is greatly improved on argon ion damaged substrates which have been additionally exposed to hydrogen at −150 V for 3 min. These experiments illustrate that hydrogen interacts with defects in InP, preventing their propagation during regrowth, and improving the photoluminescence quality of regrown quantum wells.
TL;DR: In this article, the variation of surface stoichiometry due to hydrogen ion treatments appears to be similar for both oxidized AlGaAs and GaAs surfaces, as examined by Auger electron spectroscopy.