Modulation spectroscopy is a powerful method for the study and characterization of a large number of semiconductor configurations, including bulk/thin film, microstructures (heterojunctions, quantum wells, superlattices, quantum dots), surfaces/interfaces and actual device structures in addition to semiconductor growth/processing. Furthermore, the influence of external perturbations such as temperature, electric fields, hydrostatic pressure, uniaxial stress, etc. can be investigated. This optical technique utilizes a very general principle of experimental physics, in which a periodically applied perturbation (either to the sample or probe) leads to sharp, derivative-like spectral features in the optical response of the system. Because of the richness of the derivative-like spectra, the information in the lineshape fits, room temperature performance and relative simplicity of operation this method is becoming increasingly more important as a tool to study these materials and structures. This article will review developments in the field during the last decade.

Modulation spectroscopy of semiconductors: bulk/thin film, microstructures, surfaces/interfaces and devices

We show how an empirical pseudopotential approach, fitted to bulk and interfacial reference systems, provides a unified description of the electronic structure of random alloys (bulk and epitaxial), superlattices, and related complex systems. We predict the composition and superlattice-period dependence of the band offsets and interband transitions of InAs/GaAs systems on InP and GaAs substrates.

Atomistic description of the electronic structure of In x Ga 1 − x As alloys and InAs/GaAs superlattices

Two new methods, based on the 3-point method and a Kramers-Kronig transformation, were recently published for estimating the energy, broadening, phase, and amplitude of critical points in modulated reflectance spectra which are describable by Aspnes' third derivative functional form. The use of the techniques is demonstrated by applying them to example experimental spectra, which are photoreflectance measurements of stress-induced splitting of the direct band gap E o transition in bulk GaAs. The results are compared and contrasted with those obtained from a least-squares fit of a theoretical model to the experimental spectra.

Estimating Critical-Point Parameters of Modulated Reflectance Spectra

Magnetotransport and magneto-optical measurements on InxGa1−xAs/InyAl1−yAs modulation-doped strained double quantum wells with a 100 A In0.8Ga0.2As well and a 100 A In0.53Ga0.47As quantum wells separated by a 35 A In0.25Ga0.75As potential barrier were carried out to investigate the electrical and the optical properties of the electron gas in the quantum wells. The Shubnikov-de Haas measurements at 1.5 K demonstrated clearly the occupation of three subbands in the quantum wells by a two-dimensional electron gas. The electron effective masses determined from the slopes of the cyclotron resonance peak energies as a function of the magnetic field were 0.06171 and 0.05228me. The electronic subband energies, the subband energy wavefunctions, and the Fermi energy in the quantum wells were self-consistently calculated a transfer matrix method taking into account the exchange-correlation effect, the strain effect, and the nonparabolicity effect, and the results of the cyclotron resonance measurements qualitatively...

/pdf/magnetotransport-magneto-optical-and-electronic-subband-3jsk3psdh6.pdf

Magnetotransport, magneto-optical, and electronic subband studies in inxga1-xas/inyal1-xas modulation-doped strained double quantum wells

We report a detailed analysis of room‐temperature photoreflectance data of four InxGa1−xAs/AlyGa1−yAs undoped strained single quantum wells with x≊0.20 and y≊0, 0.05, 0.10, and 0.20. We have compared our results with theoretical calculations based on an effective mass formalism, where possible variations of well and barrier composition and thickness have been included. For all the samples studied we have identified both allowed and forbidden transitions in the spectra and obtain good fits assuming a conduction‐band offset Qc of 60%±5%. This detailed analysis shows for the first time that room‐temperature photoreflectance measurements alone can be used to determine the well composition and thickness together with the barrier composition and the barrier offset.

H. Monkoc

Papers

Transmission and photoreflectance spectra in highly strained InGaAs-GaAs multiple quantum wells