In Kim

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.

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.

The characteristics of an In0.5Ga0.5P and In0.5Ga0.5P/GaAs heterojunction grown on a (100) GaAs substrate by liquid‐phase epitaxy

The growth of a high‐quality In0.5Ga0.5P/GaAs heterostructure on a (100) GaAs substrate by liquid‐phase epitaxy is demonstrated. This has been achieved by controlling the vaporizing time of phosphorus after the melt saturation procedure. The photoluminescence spectra of In0.5Ga0.5P/GaAs heteroepitaxial layers show that the major residual acceptor impurity is either carbon or silicon. The measured values of the conduction‐band discontinuity ΔEc and the fixed interface charge density σi for a In0.5Ga0.5P/GaAs heterostructure are 110 meV and 1×1011 cm−2, respectively. Only one electron trap with a thermal activation energy of Ea=0.32 eV, which is thought to be related to the anion vacancy, is found in Sn‐doped In0.5Ga0.5P (n∼1×1017 cm−3) layers.

Luminescence properties of heavily carbon doped GaAs

Carbon‐doped GaAs epilayers with concentrations as high as 1.8×1020 cm−3 were studied by photoluminescence (PL) spectroscopy. A shoulder is observed at 1.495 eV in 17 K PL spectrum of the heavily C‐doped sample grown on semi‐insulating substrate. But the shoulder occurs at different energies when the substrate conductivity is changed. The shoulder is found to originate from the substrate luminescence. Identifying the origin of the shoulder, the true Fermi level of p+‐GaAs is determined and the band gap narrowing due to heavy doping is quantified.

Amphoteric behavior of germanium in In0.5Ga0.5P grown by liquid phase epitaxy

Properties of Ge‐doped In0.5Ga0.5P grown by liquid phase epitaxy were investigated by Hall effect, capacitance‐voltage, photoluminescence, and electroluminescence measurements. The Ge dopant in InGaP shows amphoteric behavior with a compensation ratio (Na/Nd) of about 0.4. The activation energies of donor and acceptor were measured to be 47 and 58 meV, respectively. The deep acceptor transition related to Ge complex is also observed by luminescence measurements.

Effect of oxygen on the electrical and optical properties of In0.5Ga0.5P grown by liquid‐phase epitaxy

The effect of oxygen on the electrical and optical properties of In0.5Ga0.5P epitaxial layers grown on (100) GaAs by liquid‐phase epitaxy has been investigated by adding Ga2O3 to the growth melt. As the amount of Ga2O3 increases, the carrier concentration at 300 K decreases from 4×1016 to 4×1015 cm−3 and the Hall mobility at 77 K increases from 2400 to 4000 cm2/V s. The photoluminescence at 17 K shows that the peak intensity of an extrinsic transition in the In0.5Ga0.5P layer is reduced when Ga2O3 is added to the growth melt. These facts indicate that the main effect of Ga2O3 is the reduction of impurity concentration in the growth melt. In the In0.5Ga0.5P layer grown from the Ga2O3‐added growth melt, the same deep trap, with an activation energy of 0.29 eV, as in an undoped layer is observed but the trap density is decreased. This implies that the deep trap is not due to a simple intrinsic defect, but related to an impurity.

Electrical characterization of partially relaxed InxGa1−xAs/GaAs multiple quantum well structures

Electronic properties of partially relaxed InxGa1−xAs/GaAs multiple quantum well (MQW) structures are investigated using capacitance–voltage (C–V) profiling and deep level transient spectroscopy (DLTS). As the In composition becomes large, the depletion of carriers confined in QWs and the concentration of dislocation-related deep traps are increased. The carrier depletion is observed to occur predominantly in the QWs adjacent to the bottom layer. This depletion is believed to be due to electron capture at the acceptor-like misfit dislocation-related traps. Our results thus show that the C–V and DLTS measurements, combined with the numerical simulation of C–V profiles, can be used to study the influence of nonuniformly distributed misfit dislocations on the carrier distribution in MQW structures.

Reduction of as carryover by PH3 overpressure in metalorganic vapor-phase epitaxy

Abstract InGaAs/InP superlattices were grown to analyze the As carryover at the InP-on-InGaAs interface in metalorganic vapor-phase epitaxy. The analysis through the double crystal X-ray diffractometry and the subsequent simulation revealed that a InAsP transient layer is formed at the interface due to As carryover to the InP layer. The change of PH 3 flow rate during the growth interruption is found to be effective in controlling the desorption of As from the deposits on the reactor wall. It is believed that the increase of PH 3 flow rate accelerates the As desorption and thus the As depletion is completed in a shorter time. In addition, the increased amount of desorbed As helps to protect the InGaAs surface during PH 3 flow. The high PH 3 flow and the corresponding interruption time provide nearly As-free InP-on-InGaAs interface.

Optimization of Threshold Current Density for Compressive-Strained InGaAs/GaAs Quantum Well Lasers

The threshold current density (Jth) of compressive-strained InGaAs/GaAs quantum well (QW) lasers is investigated theoretically as a function of the well thicknes Lz and the well number. Lz is varied from 50 to 100 A. The optical gain is calculated with the band-mixing effects taken into account. The optimum QW thickness is determined to be about 70 A. The optimum well numbers are shown to be a function of cavity lengh.

MATRIX METHOD FOR THE X-RAY ROCKING CURVE SIMULATION

A matrix representation is developed for the solution of the Takagi–Taupin equations of x-ray diffraction. By the virtue of its unimodular property, the solution matrix substantially reduces the calculation time for the superlattice (SL) structure with a large periodicity. Also, the simplified form of the solution makes it easier to understand and quantify the inherent properties of the x-ray diffraction such as the interference fringes and the SL peaks.