Yong Tak Lee

Influence of dielectric deposition parameters on the In0.2Ga0.8As/GaAs quantum well intermixing by impurity-free vacancy disordering

We investigated the influence of the deposition parameters of SiOx and SiNx capping layers in the plasma-enhanced chemical vapor deposition on the band gap energy shift of the In0.2Ga0.8As/GaAs multiple quantum well (QW) structures induced by impurity-free vacancy disordering. The investigated deposition parameters were deposition pressure, deposition temperature, and rf power. A blueshift of photoluminescence (PL) peak energy up to 161 meV was observed after rapid thermal annealing at 950 °C for 50 s in the samples capped with SiOx deposited at 1.5 Torr. We observed that the blueshift of the PL peak energy increased greatly with the increase of deposition pressure and slightly with the decrease of deposition temperature. The influence of rf power was found to be negligible. All these dependences were related to the porosity in the dielectric capping layers in the QW intermixing.

Effects of rapid thermal annealing on the optical properties of 1.3 μm InGaAlAs multiquantum wells grown by digital-alloy molecular-beam epitaxy

We investigated the effect of rapid thermal annealing (RTA) on the optical properties of digital-alloy 1.3 μm InGaAlAs multiquantum-well structure grown by molecular-beam epitaxy at RTA temperature (TRTA) in the range of 400 °C–675 °C. Photoluminescence (PL) peak intensity taken at room temperature rose drastically at TRTA above 625 °C, which increased up to ∼500 times larger at TRTA of 650 °C and RTA time of 60 s than that of as-grown sample without any significant shift of PL peak wavelength. This extraordinary increase of PL peak intensity at TRTA⩾625 °C is attributed to the curing of nonradiative centers mainly in InAlAs grown at a lower temperature than its congruent temperature, and partially at the heterointerfaces between InGaAs/InAlAs short-period superlattices.

Molecular Beam Epitaxial Growth of High-Quality InP/InGaAs/InP Heterostructure with Polycrystalline GaAs and GaP Decomposition Sources.

A high-quality InP/InGaAs/InP double heterostructure was grown by molecular beam epitaxy (MBE) with polycrystalline GaAs and GaP decomposition sources for group V elements. By rapidly changing the cell temperature of GaAs and GaP decomposition sources during the growth switching period from InP to InGaAs and vice versa, a parasitic contamination-free InP/InGaAs/InP double heterostructure was obtained. The photoluminescence linewidths are 4.8 meV at 9 K for InGaAs on InP, and 1.76 meV at 9 K for InP on InGaAs. The X-ray rocking curve linewidth of InGaAs is as low as 20 arcsec without side lobes. These photoluminescence (PL) and X-ray measurement results are comparable to the best MBE data ever reported. Secondary ion mass spectroscopy depth profiles indicate that the contaminations due to the memory effect of group V elements are suppressed below 3 orders of magnitude and the parasitic gallium incorporation from polycrystalline GaAs decomposition sources is below 5 orders of magnitude, which are the best results obtained by MBE so far.

Lateral composition modulation in GaP/InP short-period superlattices grown by solid source molecular beam epitaxy

Transmission electron microscopy (TEM) is employed to investigate the structural properties of (GaP)/(InP) short-period superlattices (SPS) grown at temperatures in the range of 425–490 °C by solid source molecular beam epitaxy. TEM results show that lateral composition modulation (LCM) is formed in the SPS layers grown at temperatures above 460 °C. Transmission electron diffraction results show that CuPt ordering occurs in all samples. It is shown that the degree of order increases, reaches a maximum at 460 °C, and then decreases, as the growth temperature increases. Photoluminescence examination (at 9 K) shows that the samples experience a reduction in band gap, which is in the range of 55–221 meV, as the growth temperature increases. The reduction is attributed to the combined effects of the LCM and CuPt-type ordering.

Effects of rapid thermal annealing on the optical properties of In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells with InGaAs and dielectric capping layers

We investigated the effects of InGaAs and dielectric (SiO2 and Si3N4) capping layers on the intermixing behavior of InGaAs/InAlAs multiple quantum wells (MQWs) after rapid thermal annealing (RTA). With a fixed RTA time of 45 s, no appreciable shift of photoluminescence (PL) peak energy was observed in the samples annealed up to 800 and 850 °C for the SiO2- and Si3N4-capped MQWs, respectively. But they exhibited a significant improvement of PL intensity without a broadening of the PL spectra after the RTA. After an RTA at 900 °C for 45 s, a blueshift of 17 meV and a redshift of 25 meV were observed for the SiO2- and Si3N4-capped MQWs, respectively. Microstructures of the InGaAs/InAlAs MQWs observed by cross-sectional transmission electron microscopy before and after RTA reveal that the above improvement of PL intensity is associated with the curing of nonradiative recombination centers in the course of the relaxation of vertical composition modulation along the growth direction in the InGaAs well and the I...

Dependence of band gap energy shift of In0.2Ga0.8As/GaAs multiple quantum well structures by impurity-free vacancy disordering on stoichiometry of SiOx and SiNx capping layers

We have investigated the effects of the stoichiometry of SiOx and SiNx capping layers on the band gap energy shift induced by impurity-free vacancy disordering of the In0.2Ga0.8As/GaAs multiple quantum well structures. The stoichiometry of the SiOx and SiNx capping layers was changed by varying the flow rate of silane (SiH4) gas, and argon gas was employed as the carrier gas of the diluted SiH4 gas to eliminate any possible incorporation of nitrogen into the deposited film when nitrogen gas is employed as the carrier gas. A blueshift of photoluminescence peak of up to 112 meV is observed after rapid thermal annealing at 950 °C for 50 s from the sample capped with SiOx (provided with a SiH4 flow rate of 20 sccm). It is observed that the magnitude of the blueshift increases with the decrease of SiH4 flow rate for the SiOx and SiNx capping layer because of the increased porosity of dielectric capping layers. The insertion of intermediate GaAs cap layer reduces the band gap energy shift irrespective of the Si...

Design and Fabrication of 1.35-

We report full digital-alloy In(Ga1-zAlz)As/InP multiple-quantum well 1.35-μm laser diodes using molecular beam epitaxy. The wells and barriers consist of five pairs of InGaAs/InAlAs (1.5 nm/0.375 nm) and four pairs of InGaAs/InAlAs (0.66 nm/0.98 nm). The separate confinement layer consists of two 60 pairs of InGaAs/InAlAs (0.66 nm/0.98 nm) and makes for an optical confinement factor of 7.07%. We obtained a continuous wave of 200 mW from a single cleaved facet of 1.6-mm long broad area LDs, with 100-μm aperture width at 10°C, and high characteristic temperature T0 of 70 K. In this paper, we find that, with the MBE, the full digital-alloy technique makes bandgap engineering possible through the entire LD structure with only InGaAs/InAlAs short-period superlattices pairs.

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The structural and optical properties of lateral composition modulation (LCM) in (InP)n/(GaP)n short-period superlattice grown by molecular beam epitaxy were studied with transmission electron microscopy (TEM) and photoluminescence (PL) at the growth temperature (T/sub g/) of 425 and 490/spl deg/C for n = 1, 1.7, and 2. LCM occurs only in a [1-10] direction at T/sub g/ = 490/spl deg/C for n = 1 and 2. On the contrary, LCM occurs both in [1-10] and [110] directions, parallel to [100] direction, at T/sub g/ /spl ges/ 425/spl deg/C for n = 1.7. This is due to the stronger induction of LCM in tensile strain (/spl sim/-10% for n = 1.7) than in compressive strain (/spl sim/6% for n = 1 and 2). The 9 K-PL measurements show that the LCM experiences the reduction of bandgap up to /spl sim/345 meV as both n and T/sub g/ increase. This is the best data ever reported so far. The origin of bandgap shrinkage is mainly attributed to LCM along with the contribution of CuPt-type ordering.

Laser Diodes With Full Digital-Alloy InGaAlAs MQW

We studied the impurity-free vacancy diffusion (IFVD) of In0.2Ga0.8As/GaAs multi-quantum well (MQW) structures for advanced optoelectronic devices and their integration. To gain deeper insight in IFVD, the influence of the plasma enhanced chemical vapor deposition parameters, such as SiH4 flow rate, deposition temperature, deposition pressure and rf power, of SiOx and SiNx capping layers on the band gap energy shift induced by IFVD was investigated. We observed that the magnitude of the blue shift increases with the decrease of SiH4 flow rate for SiOx and SiNx capping layers. The blue shift of the PL peak energy increases greatly with the increase of deposition pressure and slightly with the decrease of deposition temperature. The influence of rf power was found to be negligible. All these dependences are related to the porosity in the dielectric capping layers in the QW intermixing. We fabricated the wavelength shifted ridge-waveguide InGaAs/GaAs MQW lasers with 967, 946 and 927 nm emission wavelengths that have undergone IFVD using SiO2 capping layers at different annealing temperatures of 850, 900 and 950 °C, respectively. Also, multi-wavelength InGaAs/GaAs MQW lasers by the area-selective IFVD using different stoichiometric SiOx capping layers were studied. The lasing wavelength difference of about 31 nm is obtained between the ridge-waveguide laser diodes fabricated with the MQWs that had undergone the same thermal treatments using the SiOx film provided with SiH4 flow rates of 20 and 300 sccm.

Structural and optical properties of lateral composition modulation in (GaP)/sub n//(InP)/sub n/ short-period superlattice

We fabricated ridge-waveguide laser diodes with In0.2Ga0.8As/GaAs multiple quantum wells (MQWs) that have undergone impurity-free vacancy disordering (IFVD) using the SiO2 capping layer. The SiO2-capped MQW samples were annealed by rapid thermal annealing (RTA) at different temperatures. The magnitude of the blueshift estimated by the shift of photoluminescence peak energy increases with the increase of RTA temperature due to the enhanced interdiffusion of the MQWs. The electrical characteristics and lasing performance of the annealed laser diodes were compared with those of the as-grown laser diode. The operation wavelengths of 967, 946 and 927 nm with device performance comparable to that of the as-grown device were obtained in the laser diodes fabricated by the MQWs that have undergone IFVD at 850, 900 and 950 °C for 50 s, respectively. Thus, the RTA for the IFVD employed to fabricate wavelength-shifted laser diodes is believed not to seriously degrade the electrical and optical properties of the devices.