Optical properties of high‐quality InGaAs/InAlAs multiple quantum wells

We have measured the narrowest half‐width at half‐maximum photoluminescence linewidth of 2.8 meV, in 40‐period lattice‐matched In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells, grown by molecular‐beam epitaxy with growth interruption. A simple analysis of the linewidth suggests that the structure has near perfect interfaces. Temperature‐dependent photoluminescence linewidth data indicate impurity incorporation due to the growth interruption. However, the high quality of the multiple quantum well is not impaired as is seen in the room‐temperature absorption data, where excitonic features up to n=3 sublevel are clearly seen. Carrier lifetime in this multiple‐quantum‐well system has been measured, we believe for the first time, using the picosecond photoluminescence correlation technique. A lifetime of 860 ps is obtained, which is similar to the value obtained for high‐quality GaAs/AlGaAs and In0.53Ga0.47As/InP quantum wells. This further confirms the high quality obtained in this ternary material system using growth interruption.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70406/2/JAPIAU-69-5-3219-1.pd

Subpicosecond photoresponse of carriers in low‐temperature molecular beam epitaxial In0.52Al0.48As/InP

Femtosecond time‐resolved reflectivity and photoconductive switching measurements have been made of In0.52Al0.48As grown by molecular beam epitaxy on (100) InP substrates at growth temperatures ranging from 150 to 480 °C. A response/switching time of ∼400 fs is measured in the sample grown at 150 °C. Temperature‐dependent measurements shed light on the nature of the material producing the ultrafast response.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71065/2/APPLAB-57-15-1543-1.pd

Erratum: ‘‘Ellipsometric characterization of In0.52Al0.48As and of modulation doped field effect transistor structures on InP substrates’’ [Appl. Phys. Lett. 62, 1411 (1993)]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69682/2/APPLAB-63-1-121-1.pd

In‐plane hole effective masses in InxGa1−xAs/Al0.15Ga0.85As modulation‐doped heterostructures

We have determined the strain dependence of the in‐plane hole effective mass in pseudomorphic Inx Ga1−x As/Al0.15 Ga0.85As modulation‐doped heterostructures by low‐temperature Shubnikov–de Haas measurements. An effective mass equal to 0.18m0 is measured for x=0.2. The measured values are in good agreement with theoretical calculations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70045/2/APPLAB-54-23-2345-1.pd

Demonstration of all‐optical modulation in a vertical guided‐wave nonlinear coupler

The performance characteristics of an AlGaAs dual waveguide vertical coupler with a nonlinear GaAs/AlGaAs multiquantum well coupling medium are demonstrated. The structure was grown by molecular beam epitaxy and fabricated by optical lithography and ion milling. The nonlinear coupling and modulation behavior is identical to that predicted theoretically. The nonlinear index of refraction and critical input power are estimated to be n2=1.67×10−5 cm2/W and Pc=170 W/cm2, respectively. This device also allows reliable measurement of the nonlinear refractive index for varying quantum well and optical excitation parameters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69681/2/APPLAB-52-14-1125-1.pd

Refractive index and electro‐optic effect in compressive and tensile strained quantum wells

The effects of biaxial compressive and tensile strain on the excitonic resonances and associated changes in refractive index and electro‐optic effect in quantum wells have been calculated and measured. Theoretical calculations include the important heavy‐hole–light–hole band mixing effects. It is seen that the excitonic contributions dominate near the band edge. With increasing compressive strain the linear electro‐optic effect is slightly increased, while the quadratic effect is greatly enhanced. The effects are reversed in quantum wells under tensile strain.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70690/2/JAPIAU-69-7-4071-1.pd

Area-Selective Disordering Of Multiple Quantum Well Structures And Its Applications To All-Optical Devices

A technique of impurity-free vacancy-induced disordering of GaAs/AlGaAs multiquantum wells (MQW) that is area selective, very reliable, and highly reproducible, has been developed. The localized compositional disordering is induced by rapid thermal annealing of the sample after it has been coated with a thin film of \u27\u27spin-on\u27\u27 glass and prebaked at 400 degrees C in a high purity nitrogen:oxygen (78:22) atmosphere. In order to self-consistently determine the diffusion coefficient of the Al and Ga atoms, the photoluminescence peak is fitted to the n=1 electron to heavy hole transition that corresponds to an error function potential profile caused by the diffusion. The process has been used to integrate two optical devices on a MQW structure. One is a nonlinear directional coupler all-optical switch, and the other is an integrated Mach-Zehnder all-optical modulator. The switching characteristics of the devices were measured using the conventional pump-probe measurement technique

Structural characterization of low‐temperature molecular beam epitaxial In0.52Al0.48As/InP heterolayers

A systematic study of the structural quality and arsenic content of as‐grown In0.52Al0.48As/InP layers deposited on InP by molecular beam epitaxy at temperatures between 150 and 450 °C was performed using transmission electron microscopy and particle‐induced x‐ray emission. We found that the amount of As incorporated in the layers generally increases with decreasing growth temperature, with the crystalline quality of the layers being good at growth temperatures higher than 200 °C. At 150 °C, a large density of pyramidal defects is formed, the defects are related to the very large amount of excess As incorporated into the layer. The mechanisms leading to the formation of these defects are discussed. At 200 °C, however, the amount of excess As is lower than expected, and wavy streaks of diffuse scattering are seen in electron diffraction. It is shown that small ordered domains of the CuPt type on the group III atoms are responsible for these features.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70657/2/APPLAB-60-8-989-1.pd

High resolution laser spectroscopy of relaxation and the excitation lineshape of excitons in GaAs quantum well structures

A new class of measurements on GaAs quantum well structures based on frequency domain nonlinear laser spectroscopy is described. Room temperature measurements of the excitation relaxation show an interference effect in the lineshape which is interpreted as a shift in exciton frequency. Low temperature measurements on the localized exciton provide an excitation lineshape which eliminates the effects of inhomogeneous broadening and shows the presence of spectral diffusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28631/1/0000445.pd

Application of lattice matched and strained quantum well systems to high performance modulators and detectors.

The ability of molecular beam epitaxy to produce layered structures on an atomic level has facilitated the study of novel properties of quantum well heterostructures for use in optoelectronic integrated circuits. The study of biaxial compressive and tensile strain on the excitonic resonances and the associated changes in refractive index and electro-optic effect in quantum wells represents the first experimental observation of this effect. The results clearly indicate the enhancement of the electro-optic coefficients with compressive strain. The changes, though manifested in the linear electro-optic coefficient, r\sb{41}, are dramatically observed in the quadratic electro-optic coefficient, s\sb{11}-s\sb{12}. The experimental study is compared with theoretical calculations and shows good agreement. A study of the performance and modulation characteristics of pseudomorphic InP-based compressive and tensile strained In\sb xGa\sb{1-x}As (0.45 $\le\ x \le$ 0.70) quantum well lasers is also undertaken. The threshold current is extremely sensitive to the magnitude and sign of the biaxial strain, as predicted by theory. Measured threshold values range from 680-2700 A/cm\sp2, comparable with the best reported to date. Large signal response is obtained from broad area devices made with this material and the results indicate that the spontaneous lifetime at threshold increases from $\sim$3 ns for the lattice matched system to $\sim$20 ns for the compressively strained system. These values are comparable to those obtained for double heterostructure lasers, while the higher values are indicative of greater quantum confinement. An analysis of the intrinsic and extrinsic limitations of high speed multiple quantum well modulators is also completed. The extrinsic limitations, are identified and the process fabrication is modified to bypass these limitations. Intrinsic limitations are calculated and the device structure altered to study these limitations. These changes have allowed the fabrication of devices with modulation bandwidths approaching 15 GHz. The final study involved the measurement of the noise suppression and signal enhancement properties of dual In\sb{0.53}Ga\sb{0.47}As/InP MSM photodiodes integrated with a leaky mode In\sb{0.52}Al\sb{0.48}As waveguide directional coupler, and an electro-optic phase shifter using single step epitaxy. A noise suppression of 11 dB and signal enhancement of 1.3 dB were recorded for the MSM photodiodes at 1.3 $\mu$m.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105585/1/9135667.pdfDescription of 9135667.pdf : Restricted to UM users only