Juno Yu-Ting Huang

MOCVD-Grown Dilute Nitride Type II Quantum Wells

Dilute nitride Ga(In)NAs/GaAsSb ldquoWrdquo type II quantum wells on GaAs substrates have been grown by metal-organic chemical vapor deposition (MOCVD). Design studies underscore the importance of nitrogen incorporation to extend the emission wavelength into the 1.5 mum region as well as increase the electron confinement, given the material strain relaxation limitations. These studies also indicate that the Sb content of the GaAs1-xSbx hole well is required to be greater than x ~ 0.2, to provide adequate hole confinement (i.e., DeltaEnu > 150 meV). Photoluminescence (PL) and electroluminescence (EL) studies are used to characterize the optical transitions and compare with a ten-band \bm k.p simulation. We find that the lowest energy type II transition observed is in good agreement with theory. Preliminary results are presented on diode lasers with two- and three-stage ldquoWrdquo-active regions that exhibit emission that is blue-shifted from the PL, due to charge separation and carrier band-filling of higher energy transitions. Further structure optimization, including multiple-stage (eight to ten W-stages) active regions is required to lower the threshold carrier density and minimize carrier band-filling and built-in electric field effects resulting from charge separation. Dilute nitride materials, such as GaAs1- y-z Sby Nz /InP, are also under development offering potential for wavelength extension into the mid-IR employing InP substrates.

Deep-Etched Native-Oxide-Confined High-Index-Contrast AlGaAs Heterostructure Lasers With 1.3

Using a modified, O2-enhanced nonselective wet thermal oxidation process, deep-etched ridge waveguides in AlGaAs heterostructures containing lambda = 808 nm InAlGaAs single quantum well or aluminum-free lambda = 1.3 mum GaAsP/InGaAsN dilute nitride multi-quantum-well active regions have been directly oxidized to effectively provide simultaneous electrical isolation, interface state passivation, and sidewall roughness reduction. The resulting high- index-contrast (HIC) ridge waveguide (RWG) diode lasers show improved performance relative to conventional shallow-etched devices owing to both strong optical confinement and the complete elimination of current spreading, with 5 mum stripe width dilute- nitride devices showing up to a 2.3 times threshold reduction and strong index guiding for kink-free operation. Oxidation of an AlGaAs graded-index separate confinement heterostructure is studied for varying O2 concentrations, and the interface passivation effectiveness of the native oxide is studied through comparison with deposited SiO2 and via a study of the stripe-width dependence of internal quantum efficiency and modal loss. The HIC RWG structure is shown to enable the operation of half-racetrack-ring- resonator lasers with a bend radius as small as r = 6 mum.

\mu

A GaAsSbN-GaAsSb-InP type-II ldquoWrdquo quantum well (QW) structure is proposed for achieving emission in the mid-infrared (IR) wavelength region. Simulation studies based on the band anticrossing model and a 10-band k-p Hamiltonian demonstrate that emission wavelengths as long as 3 mum could be achieved on an InP substrate, limited primarily by strain relaxation considerations. The incorporation of nitrogen into GaAsSb grown on InP leads to band-gap narrowing and a deepening of the conduction band offset. The energy band structure, interband emission wavelengths, and optical matrix elements are evaluated for a GaAsSbN-GaAsSb-InP SL structure design. A structure design utilizing the lowest Sb content for the GaAsSbN electron wells and the highest Sb content for the GaAsSb hole wells, within strain limitations, provides the longest wavelength emission. The electron and hole effective masses of bulk GaAsSbN are extracted from the computed energy band structure as a function of Sb and N composition. The electron effective mass of GaAsSbN is found to remain nearly constant with N for low N-composition alloys. The heavy- and light-hole effective masses decrease slightly with increasing N composition.

m Dilute-Nitride Quantum Wells

GaAsSbN∕InP strained layer superlattice (SL) structures have been grown using low-temperature metal organic chemical vapor deposition with N composition varying from 0.6% to 1.6%. High-resolution x-ray diffraction measurements indicate that GaAsSbN∕InP SLs with defect-free layers and abrupt interfaces were achieved. Low-temperature photoluminescence measurements reveal that nitrogen incorporation into the GaAsSbN layers extends the emission wavelength, increases the conduction band offset, and dramatically changes the As∕Sb ratio. In parallel with the experimental efforts, simulation studies using a ten-band k∙p model are carried out to correlate the emission properties of these SL structures with experiment. Photoluminescence measurements indicate an emission wavelength redshift with respect to the simulated values.

GaAsSbN–GaAsSb–InP Type-II “W” Quantum Wells for Mid-IR Emission

High performance native-oxide-confined high-index-contrast (HIC) ridge waveguide (RWG) diode lasers are fabricated in a strain-compensated In0.4Ga0.6As single quantum well structure by employing a deep dry etch plus nonselective O2-enhanced wet thermal oxidation process. The thermal native oxide grown on the etch-exposed RWG sidewalls of the Al0.74Ga0.26As waveguide cladding layers and GaAs core with GaAsP–InGaAs quantum well provides both strong optical and electrical confinements for the active region. Due to a smoothing of sidewall roughness by the O2-enhanced oxidation, the lasers exhibit a low internal loss in αi=7.2 cm−1 for a w=7.2 μm narrow stripe HIC RWG structure, only 53% larger than that of w=87.2 μm broad-area devices, enabling their room temperature operation at a low 300 A/cm2 threshold current density.

Characteristics of dilute-nitride GaAsSbN∕InP strained multiple quantum wells

The thermal annealing of GaAsSbN∕InP strained multiple quantum wells (MQWs) grown by metal organic chemical vapor deposition was investigated. Photoluminescence peak intensity and linewidth changes indicate a significant improvement in optical quality of the GaAsSbN∕InP MQWs upon annealing. We find no significant annealing-induced blueshift of the optical transitions, which confirms the theoretical expectation that a change in the nearest-neighbor configuration nitrogen atoms has negligible effect on the band gap of GaAsSbN. The evolution of (400) x-ray diffraction rocking curves with thermal treatment of the samples was consistent with the constituent redistribution in the GaAsSbN QW.

Native-oxide-confined high-index-contrast λ=1.15 μm strain-compensated InGaAs single quantum well ridge waveguide lasers

A modified wet thermal process is used to oxidize both GaAs waveguide and GaAsP/InGaAsN MQW layers of deeply-etched ridge waveguide lasers, providing up to a 2.3 times threshold reduction and strong index-guiding for kink-free operation

Annealing of dilute-nitride GaAsSbN∕InP strained multiple quantum wells

Pseudomorphic GaAs1?ySby quantum wells with 0.16 ? y ? 0.69 on (0?0?1) InP substrates have been grown using metal?organic chemical vapour deposition. High resolution x-ray diffraction and transmission electron microscopy analysis are used to quantify the layer thicknesses and compositions. Studies of the optical properties suggest that a transition from type-I to type-II band alignment occurs at an antimony concentration of approximately y = 0.30. The interband optical transition energies simulated using a ten-band k ? p Hamiltonian are compared with the experimental values deduced from photoluminescence spectroscopy. The valence band offset bowing parameter is evaluated in the context of the experimental transition energies. For low Sb-contents, reasonable agreement (<7% deviation) is achieved between theory and experiment for the primary optical transitions. However, at higher Sb-content, there is significant deviation between the measured transition energies and the k ? p based theory, possibly a result of a non-ideal interface and/or heterogeneous ternary well.

High-Index-Contrast Oxide-Confined GaAsP/InGaAsN Multi-Quantum-Well Ridge Waveguide Lasers

The time evolution of the photoluminescence (PL) of 1300-nm emitting InGaAsN/ GaAs/GaAsP strain-compensated single quantum well (QW) in the temperature range of T 1/4 10 K - 300 K is investigated. The PL spectra observed at the early stages of carrier recombination is dominated by two transitions. These two transitions are identified as the first quantized electron state to heavy-hole state (e1-hh1) and electron to light-hole state (e1-lh1) from the analysis of polarized photocurrent measurements in combination with k · p simulation of the band structure. At longer time delays, the dilute-nitride QW exhibits carrier localization at low temperatures and faster recombination time at higher temperatures. The PL dynamics characteristics observed in the InGaAsN QW are different from those measured from the InGaAs QW.

Characteristics of strained GaAs1−ySby (0.16 ≤ y ≤ 0.69) quantum wells on InP substrates

An electron effective mass (m_e*) of (0.11plusmn0.015)m₀ is experimentally determined in high indium content InGaAsN quantum well. The impact of the large m_e* in the material differential gain is analyzed through a gain model