B. Aslan

Response spectra from mid- to far-infrared, polarization behaviors, and effects of electron numbers in quantum-dot photodetectors

Photoresponse characteristics of InAs/GaAs self-assembled quantum-dot infrared photodetectors in a wide spectral region from the mid- to far-infrared are reported. Clear polarization behaviors with a dominant P-polarized response in the mid-infrared and a strong S-response in the far infrared are shown. These behaviors can be qualitatively understood in view of the quantum-dot shape of a large in-plane diameter and a small height in the growth direction. With a set of three samples, effects of the number of electrons per dot on the spectra are investigated.

Detailed characterization of a systematic set of quantum dot infrared photodetectors

The results of a detailed characterization study on a systematic set of InAs/GaAs self-assembled quantum dot infrared photodetectors are presented. A simple physical picture is also discussed to account for the main observed features. Photoresponse characteristics in a wide spectral region from the mid- to far-infrared are reported. Clear polarization behaviors with a dominant P-polarized response in the mid-infrared and a strong S-response in the far-infrared regions are shown. These behaviors can be qualitatively understood in view of the quantum dot shape of a large in-plane diameter and a small height in the growth direction. With a set of three samples, effects of the number of electrons per quantum dot on the spectra are investigated.

On the spectral response of quantum dot infrared photodetectors: Postgrowth annealing and polarization behaviors

Effects of the postgrowth rapid thermal annealing on the device properties of a multilayer InAs∕GaAs quantum dot infrared photodetector are investigated. Clear shift in the spectral photoresponse toward smaller energy region with increasing annealing temperatures is shown. Polarization behaviors of the photoresponse peaks are presented.

Quantum dots for terahertz generation.

Nanostructures made of semiconductors, such as quantum wells and quantum dots (QD), are well known, and some have been incorporated in practical devices. Here we focus on novel structures made of QDs and related devices for terahertz (THz) generation. Their potential advantages, such as low threshold current density, high characteristic temperature, increased differential gain, etc, make QDs promising candidates for light emitting applications in the THz region. Our idea of using resonant tunneling through QDs is presented, and initial results on devices consisting of self-assembled InAs QDs in an undoped GaAs matrix, with a design incorporating a GaInNAs/GaAs short period superlattice, are discussed. Moreover, shallow impurities are also being explored for possible THz emission: the idea is based on the tunneling through bound states of individual donor or acceptor impurities in the quantum well. Initial results on devices having an AlGaAs/GaAs double-barrier resonant tunneling structure are discussed.

Quantum dots for terahertz devices

Semiconductor nanostructures, such as quantum wells and quantum dots (QD), are well known, and some have been incorporated in applications. Here will focus on novel structures made of QDs and related devices for terahertz (THz) generation. Their potential advantages, such as low threshold current density, high characteristic temperature, increased differential gain, etc., make QDs promising candidates for light emitting applications in the THz region. Our idea of using resonant tunneling through QDs is presented, and initial results on devices consisting of self assembled InAs QDs in an undoped GaAs matrix, with a design incorporating GaInNAs/GaAs short period superlattice, are discussed. Moreover, shallow impurities are also being explored for possible THz emission: the idea is based on the tunneling through bound states of individual donor or acceptor impurities in the quantum well. Initial results on devices having an AlGaAs/GaAs double barrier resonant tunneling structure are discussed.

Observation of resonant tunneling through a self-assembled InAs quantum dot layer

We report on the study of resonant tunneling through a self-assembled InAs quantum dot (QD) layer using the following design: The QD layer surrounded by undoped GaAs barriers is clad by two GaInNAs∕GaAs short-period superlattice regions which serve as injector and collector of electrons. A clear observation of three- to zero-dimensional resonant tunneling is presented in electrophotoluminescence measurement results and supported with current-voltage and capacitance-voltage characteristics.