We have investigated the optical transitions in Be ␦-doped GaAs/ AlAs multiple quantum wells with various width and doping levels. The fractional dimensionality model was extended to describe free-electron-acceptor ͑free hole-donor͒ transitions in a quantum well. The measured photoluminescence spectra from the samples were interpreted within the framework of this model, and acceptor-impurity induced effects in the photoluminescence line shapes from multiple quantum wells of different widths were demonstrated.

Radiative recombination spectra of p -type δ -doped Ga As ∕ Al As multiple quantum wells near the Mott transition Photoreflectance and surface photovoltage spectroscopy of beryllium-doped Ga As ∕ Al As multiple quantum wells J. Appl. Phys. 98, 023508 (2005); 10.1063/1.1978970Effect of quantum-well confinement on acceptor state lifetime in δ -doped GaAs/AlAs multiple quantum wells Beryllium and silicon ␦-doped GaAs/ AlAs multiple quantum wells ͑MQWs͒ were designed and fabricated for selective sensing of terahertz radiation. Optical characterization of the structures by photoreflectance spectroscopy has indicated a presence of built-in electric fields-from 18 up to 49 kV/ cm depending on the structure design-located mainly in the cap and buffer layers, but do not penetrating into the MQWs region. Terahertz sensing under normal incidence via impurity bound-to-unbound transitions is demonstrated in photocurrent experiments within 0.6-4.2 THz in silicon-doped MQWs and 3.5-7.3 THz range in beryllium-doped MQWs at low temperatures.

We present a study of silicon (Si) and erbium (Er) coimplanted silica (SiO2) in which we observe, by combining high resolution scanning transmission electron microscopy and selective electron energy loss spectroscopy (EELS), a high spatial correlation between silicon nanocrystals (Si-NCs), Er, and oxygen (O) after a single high temperature (1100 °C) anneal. The observation of a spatial overlap of the EELS chemical maps of dark field (DF) images at the Er N4,5, Si L2,3, and O K edges is concomitant with an intense room temperature infrared luminescence around 1534 nm. We suggest that these observations correspond to Er–O complexes within an amorphous silicon (a-Si) shell at the Si-NC/SiO2 interface. The presence of a crystalline phase at the Si-NC center, verified by high resolution electron micrographs and DF diffraction contrast images and the low solubility of Er in crystalline Si (c-Si) would tend to suggest a preferential Er agglomeration toward the Si-NC/SiO2 interface during formation, particularly when high concentrations of both Si and Er are obtained in a narrow region of the SiO2 after coimplantation. The absence of narrow Stark related features in the Er emission spectrum at low temperature and an inhomogeneous broadening with increasing temperature, which are characteristic of Er confined by an amorphous, rather than a crystalline host further support these hypotheses. After comparing the luminescence to that from a SiO2:Er control sample prepared in exactly the same manner but without Si-NCs, we find that, despite the observed spatial correlation, only a small fraction (∼7%) of the Er are sensitized by the Si-NCs. We ascribe this low fraction to a combination of low sensitizer (Si-NC) density and Auger-type losses arising principally from Er ion-ion interactions.

We present the photoluminescence properties of highly Be δ-doped GaAs/AlAs multiple quantum wells at liquid nitrogen and room temperatures. Possible mechanisms of carrier recombination focusing on peculiarities of excitonic and free-carriersacceptor photoluminescence are discussed. It is estimated that for Be δ-doped GaAs/AlAs quantum wells (LW = 5 nm) the Mott transition should occur at acceptor concentration NBe some greater than 5 • 10 12 cm −2 .

Experimental results showing room temperature normal incidence mid-infrared detection by AlGaN/GaN quantum well infrared photodetectors are presented. Designed structures have intersubband transitions corresponding to wavelengths in the region of 3 and 4 µm, where strong absorption in a sapphire substrate dominates. The intersubband spectra, therefore, were characterized by electronic Raman scattering and infrared photocurrent spectroscopy. The absorption spectra agree well with theoretical predictions. Details of device fabrication are presented with sensitivity estimates for the devices.