We describe a novel method of confining carriers by deliberately creating large inhomogeneous strain patterns in a quantum well The strain modulates the band gap to provide lateral quantum confinement for excitons Here, we generate strain confinement in an InGaAs quantum well by reactive ion beam assisted etching through an overlying compressed pseudomorphic quaternary layer using etch masks patterned by electron beam lithography Photoluminescence spectra of arrays of wires and dots show red‐shifted band gaps in direct evidence of lateral confinement We compare our results to finite element calculations of the inhomogeneous strain in an InP substrate from a compressed overlayer patterned into rectangular wires

Strain-induced confinement of carriers to quantum wires and dots within an InGaAs-InP quantum well

A technique is described for the simultaneous measurement of the difference in the normal components of strain and of the shear strain in luminescent III-V material from the degree of polarization (DOP) of photoluminescence. This technique for the measurement of shear strain and of the difference in the normal components of strain in InP was calibrated by applying known external loads on the bars of InP with V grooves etched into the bars and by fitting the experimental results to two-dimensional finite-element simulations. Fits to the difference in the normal components of strain (as opposed to stress) yielded significantly smaller residues. On this basis we conclude that the DOP of luminescence is proportional to the difference in the normal components of strain.

Strain mapping by measurement of the degree of polarization of photoluminescence

We have investigated the use of thin film technology to introduce controllable and thermally stable stress into semiconductor heterostructures. Two simple schemes are used. The first scheme is to use interfacial reactions between a metal and the substrate, such as Ni, Co, Pd, and Pt on GaAs/AlGaAs. The induced stress in the structure is reproducible and controllable because the volumetric change for a given reaction is fixed, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. In the case of Ni and Co on GaAs/AlGaAs, the induced stress is thermally stable up to 600 °C. Evaporated films and reacted films are usually under tension. The second scheme is to use rf sputtered W or WNi alloy films where W or WNi is sputtered onto a negative dc biased substrate. This scheme effectively provides highly compressed films. The thermal stability depends on the concentration of Ni in the WNi alloy. Using the two schemes above, we have ...

Photoelastic waveguides and the controlled introduction of strain in III‐V semiconductors by means of thin film technology

We have developed several direct-write laser processing techniques to masklessly fabricate prototypes of waveguiding devices in GaAs/AlGaAs substrates. This flexible technology allows the rapid, successive fabrication and testing of devices such as modulators. Previously, we had reported use of this technology to fabricate low-loss single-mode passive waveguiding structures and devices. In this paper, we report the fabrication of active electro-optic modulators. These devices include an electro-optic polarization modulator, an integrated amplitude modulator consisting of a polarization modulator and an on-chip polarizer, and an integrated Mach-Zehnder interferometer. >

Rapid direct fabrication of active electro-optic modulators in GaAs

Diffusion lengths of excited carriers in a CdxZn1−xSe multiple quantum well structure were determined for temperatures between room temperature and 8 K from cathodoluminescence measurements The diffusion length was found to depend upon temperature and Cd concentration of the quantum well For the highest Cd concentration (x=043), the diffusion length increased with temperature up to 225 K and then dropped at higher temperatures Diffusion lengths were 021 μm at 8 K, 038 μm at 225 K, and 024 μm at room temperature For the well with least Cd concentration (x=024), longer diffusion lengths were obtained The nature of the diffusing carriers is also discussed

Diffusion lengths of excited carriers in CdxZn1−xSe quantum wells

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.

B. G. Yacobi

Papers

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