C. Jagannath

In situ measurements of critical layer thickness and optical studies of InGaAs quantum wells grown on GaAs substrates

Reflection high‐energy electron diffraction (RHEED) intensity oscillations have been used during molecular beam epitaxy (MBE) to accurately determine threshold layer thicknesses for two‐dimensional (2D) growth of InxGa1−xAs on GaAs for a wide range of substrate temperatures and indium compositions. InxGa1−xAs/GaAs single quantum wells were also grown by MBE and studied using low‐temperature photoluminescence (PL) spectroscopy. PL peak energy, intensity, and linewidth measurements provided information on the critical layer thicknesses for the formation of dislocations which, under our experimental conditions, were the same as the threshold layer thicknesses for 2D growth measured from the damping behavior of RHEED intensity oscillations.

Effect of heat treatment on InGaAs/GaAs quantum wells

We report on the effect of furnace annealing on 60‐A‐wide InxGa1−xAs/GaAs single quantum wells (SQWs) in the range of indium composition 0.1≤x≤0.5. Excitonic energy shifts of up to 120 meV were observed after annealing of the samples at 825 °C for 30 min. The fact that these energy shifts were strongly dependent of the indium composition in the well material was consistent with enhancement on the indium diffusion out of the wells associated with the presence of dislocations. The most dramatic changes, as a result of annealing, manifested by strain recovery were observed from the SQW with x=0.3 which as‐grown had a low dislocation density (quantum well thickness slightly exceeding the critical layer thickness for formation of dislocations).

Temperature‐dependent optical spectra of single quantum wells fabricated using interrupted molecular beam epitaxial growth

Photoluminescence excitation (PLE) and temperature‐dependent photoluminescence (PL) spectroscopies have been employed to interpret fine structure observed in the low‐temperature PL spectra of GaAs/AlGaAs single quantum wells grown by molecular beam epitaxy under conditions of interrupted growth. Multiple peaks observed in the low‐temperature PL spectra of similar samples grown by others have been held to be proof of monolayer steps in exceptionally smooth interfaces. We show that similar structure in the low‐temperature PL spectra of our samples is not intrinsic. However, PLE or higher temperature PL spectroscopy yields unambiguous evidence for the model of interface smoothing due to growth interruption.

InGaAs/GaAs strained quantum wells with a 1.3 μm band edge at room temperature

The fabrication of long‐wavelength optoelectronic devices on GaAs substrates is an attractive method for monolithic integration of optical and electronic devices on a single chip for applications in telecommunications. In this letter we describe our studies of one such scheme using a novel structure for spatially separating a portion of the biaxial compressive stress due to lattice mismatch of the layers from the well layer, and demonstrate its feasibility. High quality pseudomorphic strained InGaAs quantum wells were grown on GaAs substrates by molecular beam epitaxy with a band edge between 1.3 and 1.4 μm at room temperature. Low‐temperature photoluminescence spectroscopy as well as polarization‐dependent absorption measurements in a waveguide geometry was used to characterize the structures.

1.3 μm monolithically integrated waveguide‐interdigitated metal‐semiconductor‐metal photodetector on a GaAs substrate

An InGaAs/GaAs strained‐layer single quantum well waveguide‐photodetector combination operating at a wavelength of 1.3 μm was fabricated on a GaAs substrate. An interdigitated metal‐semiconductor‐metal detector was deposited on top of the waveguide using Ti/Pt/Au for Schottky contacts. As expected, the responsivity of the detector increased with increasing single quantum well absorption in the waveguide and was sensitive to the polarization of the incident light. For TM polarization the responsivity of the detector was an order of magnitude lower at 1284 nm, compared to TE polarization, and exhibited weak dependence on wavelength, consistent with the transmission data. These results demonstrate for the first time a monolithically integrated 1.3 μm waveguide photodetector fabricated on a GaAs substrate.

Coupling of ground and excited state excitations in GaAs under uniaxial stress

Abstract We report new experimental evidence of the exchange interaction between heavy and light excitons near the Brillouin zone center in GaAs. We have combined polarized photoluminescence excitation spectroscopy and uniaxial stress at liquid He temperatures in order to elucidate the structure of the free exciton states in low donor concentration GaAs grown by molecular beam epitaxy. The data indicate that the exchange interaction is small (deduced from the peak positions of the polarized spectra) but finite (due to the observation of level repulsion between the ground state of the light exciton and excited states of the heavy exciton at a stress of about 0.5 kbar).

High‐speed 1.3 μm InGaAs/GaAs metal‐semiconductor‐metal photodetector

A high frequency, low dark current, 1.3 μm metal‐semiconductor‐metal photodetector on GaAs is reported. The measured frequency response of this photodetector up to 10 GHz agrees with a model that assumes different collection times for electrons and holes.

Cathodoluminescence observation of metallization‐induced stress variations in GaAs/AlGaAs multiple quantum well structures

Cathodoluminescence scanning electron microscopy is utilized to investigate the stresses present underneath 0.4 μm gold layers deposited on GaAs/AlGaAs multiple quantum well structures grown by molecular beam epitaxy on GaAs substrates. Using the known stress dependence of excitonic lines in quantum wells, the magnitude of stress is determined to be about 1 kbar. The stress‐induced change in the refractive index, attributed to photoelastic effect, is about 0.01 for the structures studied in the present work.

Optical Characterization Of Single Quantum Wells Fabricated Under Conditions Of Interrupted Growth

Multiple peaks, recently observed in the low temperature photoluminescence (PL) spectra of GaAs/AlGaAs single quantum wells fabricated by momentarily interrupting the molecular beam epitaxial growth between adjacent but different semiconductor layers, have been interpreted as originating within smooth regions in the quantum well layer differing in width by exactly one monolayer. We have observed similar structure in similarly grown samples but find that low temperature PL can be misleading. However, higher temperature PL or PL excitation spectroscopy do provide unambiguous evidence for the model of interface smoothing due to growth interruption. Further, time-resolved spectra yield decay times of the individual peaks which are consistent with this interpretation.

Temperature Dependent and Time Resolved Optical Studies of Single Quantum Wells Produced by Interrupted Growth MBE

Multiple peaks, recently observed in the low temperature photoluminescence (PL) spectra of GaAs/AlGaAs single quantum wells fabricated by momentarily interrupting the molecular beam epitaxial growth between adjacent but different semiconductor layers, have been interpreted as originating within smooth regions in the quantum well layer differing in width by exactly one monolayer. We have observed similar structure in similarly grown samples but find that low temperature PL can be misleading. However, higher temperature PL or PL excitation spectroscopy do provide unambiguous evidence for the model of interface smoothing due to growth interruption. Further, time-resolved spectra yield decay times of the individual peaks which are consistent with this idea.