Weon Guk Jeong

Dense arrays of ordered GaAs nanostructures by selective area growth on substrates patterned by block copolymer lithography

GaAs has been selectively grown in a hexagonally ordered array of nanometer-scale holes with a density as high as ∼1011/cm2 by metalorganic chemical vapor deposition. This array of holes was created using block copolymer lithography, in which a thin layer of diblock copolymer was used as an etching mask to make dense holes in a 15-nm-thick SiNx film. These selectively grown nanoscale features are estimated to be 23 nm in diameter with narrow lateral size and height distributions as characterized by field-emission scanning electron microscopy and tapping mode atomic force microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots we report offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode.

The effect of strain on the interdiffusion in InGaAs/GaAs quantum wells

The effect of strain on the cation interdiffusion in InGaAs/GaAs quantum wells is described. It is found that the Fick’s diffusion equation does not properly describe the interdiffusion in the heterostructure with strained layers. It is believed that the strain changes crystal defect concentration and thus diffusivity is influenced by strain. Diffusion equation including the strain effect is formulated and solved numerically. The experimental photoluminescence peak shifts as a function of annealing time are well‐fitted by this analysis and useful parameters such as diffusivity describing InGaAs/GaAs quantum well interdiffusion are extracted.

Epitaxial growth and optical characterization of InAs/InGaAsP/InP self-assembled quantum dots

Five stacks of InAs quantum dots (QDs) with InGaAsP barriers were grown on (100) InP and luminescence characteristics were analyzed. Cross-sectional transmission electron microscopy shows that small dots with a lateral size of ∼30 nm and a height of ∼3 nm are formed with an areal density of ∼5×1010 cm−2. The QDs emit strong photoluminescence (PL) peaks in the range of 1.4–1.6 μm that can be controlled by nominal InAs thickness. The integrated PL intensity from QDs stays very high at room temperature as much as 20% of that at 10 K. At weak excitation, the carrier lifetimes are measured to be almost the same across the whole PL band at low temperature with a value of ∼4 ns and they remain at that value at room temperature. These characteristics strongly evidence that individual QDs are well isolated and have a strong carrier confinement at room temperature.

Atmospheric pressure atomic layer epitaxy : mechanisms and applications

Abstract Atomic layer epitaxy (ALE) has been adapted for hybrid use with conventional atmospheric pressure metalorganic chemical vapor deposition (MOCVD) by using organometallic precursors for the column III elements. Saturation of the growth rate to one monolayer per cycle is observed over a range of growth parameters by thermally driven and laser (or light) driven reactions. The mechanisms causing this saturation are investigated using empirical growth studies and surface reaction studies in UHV conditions. It is concluded that the useful range of ALE growth temperatures for GaAs using metal alkyls is limited by gas phase reactions which frustrate the basic saturation process. Strategies for overcoming this limitation to achieve general purpose epitaxial growth by ALE are described.

Steric hindrance effects in atomic layer epitaxy of InAs

Atomic layer epitaxy of InAs is demonstrated. Saturation of the growth rate of one monolayer per cycle is achieved at a growth temperature of 340 °C. The growth rate is found to be a strong function of trimethylindium exposure times for the same total amount of reactant exposure per cycle. There is a threshold exposure time to achieve a growth rate of one monolayer per cycle. For shorter exposure time, the growth rate saturates to sub‐one monolayer per cycle. The dependence of growth rate on exposure time is explained by steric hindrance effects of the initial adsorbate.

Room temperature operation of InGaAs∕InGaAsP∕InP quantum dot lasers

The growth conditions for InGaAs∕InGaAsP∕InP quantum dots (QDs) have been optimized and QDs of high luminescence efficiency and the room temperature operation of QD lasers emitting at ∼1.5μm have been demonstrated. Lattice-matched InGaAsP (λg=1.0–1.1μm) was used as a barrier layer for the InGaAs QDs and the emission wavelength was controlled by the QD composition. High-density InGaAs QDs with an areal density as high as 1.13×1011cm−2 have been grown. The integrated and peak intensity of the photoluminescence (PL) spectra at room temperature are as high as 25% and 10% of those at 10K, respectively. The room temperature PL peak intensity is about 50% that of a high-quality InGaAs∕InP quantum well. Room temperature, pulsed operation at ∼1.5μm has been achieved from broad area lasers with a 1mm cavity length. Threshold current density per QD stack of ∼430A∕cm2 is measured for the five-, seven-, and ten-stack QD lasers.

Carbon doping and growth rate reduction by CCl4 during metalorganic chemical‐vapor deposition of GaAs

The electrical, structural, and optical properties of GaAs grown by metalorganic chemical‐vapor deposition using CCl4 have been studied and the growth rate reduction by CCl4 under various growth conditions has been investigated. Hole concentrations ranging from 2×1016 to 1.8×1020 cm−3 have been obtained by varying V/III ratio and growth temperature. From Hall, x‐ray, and low‐temperature photoluminescence measurements, a low compensation is ensured. A growth rate reduction up to 50% has been observed. The dependence of the growth rate reduction on the growth temperature, the V/III ratio, and the CCl4 mole fraction was investigated. It is believed that the growth rate reduction is caused not by etching of solid GaAs but by reduction of Ga species through the formation of GaCl in gas phase.

CHARACTERIZATION AND DETERMINATION OF THE BAND-GAP DISCONTINUITY OF THE INXGA1-XAS/GAAS PSEUDOMORPHIC QUANTUM WELL

Single and multiple quantum well samples have been grown by atmospheric pressure metalorganic chemical vapor deposition at In compositions from 9 to 28% and layer thicknesses ranging from 15 to 140 A, depending upon the composition. Selected samples containing three quantum wells of a given composition but with different thicknesses were characterized by x‐ray double‐crystal diffractometry, low‐temperature photoluminescence, and transmission electron microscopy (TEM). Using a simulation technique based on the dynamical theory of x‐ray diffraction in concert with TEM measurements, the In composition in the quantum well as well as the thicknesses can be directly extracted. The peak positions of the photoluminescence are used to determine the strained and unstrained energy gap and the conduction band offsets associated with InxGa1−xAs of a given composition. We have found the discontinuities to be 60% of the difference in the energy gap of GaAs and strained InxGa1−xAs.

Determination of interdiffusion coefficients of cations and anions in InGaAs/InP superlattice

The interdiffusion coefficients of cations and anions in InGaAs/InP superlattices (SLs) on their respective sublattices were analyzed quantitatively. Double crystal X-ray diffraction and simulation of the rocking curves based on dynamical diffraction theory were used to measure the interface strain that develops during rapid thermal annealing. Low temperature photoluminescence (PL) measurements were also done to assess the interdiffusion through the change in ground state transition energy of the SL. Simulation with the proper selection of the interdiffusion coefficients results in proper fitting of the interface strain profile and PL transition energies. Using this method, interdiffusion behaviors of InGaAs/InP SLs with and without SiO2:P capping were analyzed. Interdiffusion coefficients of 5.8×10−17 and 2.9×10−17 cm2/s were obtained for the anion and cation sublattices respectively, when the SL without SiO2:P was annealed at 800 °C.

DETERMINATION OF AL MOLE FRACTION FOR NULL CONDUCTION-BAND OFFSET IN IN0.5GA0.5P/ALXGA1-XAS HETEROJUNCTION BY PHOTOLUMINESCENCE MEASUREMENT

Photoluminescence properties of In0.5Ga0.5P/AlxGa1−xAs heterojunctions in both staggered and straddling band alignment regimes have been investigated. From the relation between the energies of below‐band gap luminescence and Al compositions in the staggered band alignment regime, we determined the Al composition for null conduction band offset of the heterojunction as well as the conduction band offset value of In0.5Ga0.5P/GaAs heterojunction. Assuming the transitivity between the conduction band offset values, we also obtained the fraction of the band gap energy difference that is associated with the conduction band offset of an AlGaAs/GaAs heterojunction.