Optical study of electronic states in GaAsN

GaAs1-xNx alloys with small N composition (x<1%) and GaAsN/GaAs quantum wells (QWs) were studied by continuous wave photoluminescence (PL), pulse wave excitaiton PL and time-resolved PL. In the PL spectra an extra transition located at the higher energy side of the commonly reported N-related emissions was observed. By measuring the PL dependence on temperature and excitation power, the new PL peak was identified as a transition of alloy band edge-related recombination in GaAsN and delocalized transition in QWs. The PL dynamics further confirms its intrinsic nature of band edge states rather than N-related bound states.

Observation of the resonant Raman behavior of individual single-walled carbon nanotubes

The different resonant Raman scattering process of single-walled carbon nanotubes (SWNTs) has been found between the Stokes and anti-Stokes sides of the radial breathing modes (RBMs), and this provides strong evidence that Raman spectra of some special diametric SWNTs are in resonance with their electronic transitions between the singularities in the one-dimensional electronic density of states in the valence and conduction bands, and other SWNTs axe beyond the resonant condition. Because of the coexistence of resonant and non-resonant Raman scattering processes for different diametric SWNTs, the relative intensity of each RBM does not reflect the proportion of a particular SWNT.

Electro-mass multi odor sensor

For an olfactory sensor or electronic nose the task is not only to detect the object concentration, but also to recognize it. It is well known that all the elements can be identified by their charge to mass ratio e+/m. We tried to use this principle for molecular recognition. Two kinds of sensors are used simultaneously in testing. One is Quartz Crystal Microbalance (QCM) for detecting the change in mass, the other is Interdigital Electrode (IE) for detecting the change in conduction. In this paper the principle and the feasibility of this method are reported. The preliminary results on the recognition of alcohols are presented. The multisensor can be used as an instrument for research on material properties and kinetic process as well.

Electronic structure and optical property of semiconductor nanocrystallites

Semiconductor nanostructures show many special physical properties associated with quantum confinement effects, and have many applications in the opto-electronic and microelectronic fields. However, it is difficult to calculate their electronic states by the ordinary plane wave or linear combination of atomic orbital methods. In this paper, we review some of our works in this field, including semiconductor clusters, self-assembled quantum dots, and diluted magnetic semiconductor quantum dots. In semiconductor clusters we introduce energy bands and effective-mass Hamiltonian of wurtzite structure semiconductors, electronic structures and optical properties of spherical clusters, ellipsoidal clusters, and nanowires. In self-assembled quantum dots we introduce electronic structures and transport properties of quantum rings and quantum dots, and resonant tunneling of 3-dimensional quantum dots. In diluted magnetic semiconductor quantum dots we introduce magnetic-optical properties, and magnetic field tuning of the effective g factor in a diluted magnetic semiconductor quantum dot. (C) 2004 Elsevier B.V. All rights reserved.

Electro-mass olfactory multi-sensor (EMMS)

For an olfactory sensor or electronic nose, the task is not only to detect the object concentration, but also to recognize it. It is well known that all the elements can be identified by their charge to mass ratio e(+)/m. We tried to imitate this principle for molecular recognition. Two kinds of sensors are used simultaneously in testing. One is quartz crystal microbalance (QCM) for detecting the change in mass, the other is interdigital electrode (IE) for detecting the change in conduction, as an electro-mass multi-sensor (EMMS). in this paper, the principle and the feasibility of this method are discussed. The preliminary results on the recognition of alcohol by EMMS coated with lipids are presented. Meanwhile, the multi-sensor can also be used as an instrument for research on some physico-chemistry problems. The change in conduction of coated membrane caused by one absorbed molecule is reported. It is found that when a QCM is coated with membrane, it still obeys the relationship Delta F (frequency change of QCM) = K Delta m (mass change of absorbed substance) and the proportional coefficient, K, depends not only on quartz properties but also on membrane characteristics as well. (C) 2000 Elsevier Science S.A. All rights reserved.

Methods to tune the electronic states of self-organized InAs/GaAs quantum dots

After capping InAs islands with a thin enough GaAs layer, growth interruption has been introduced. Ejected energy of self-organized InAs/GaAs quantum dots has been successfully tuned in a controlled manner by changing the thickness of GaAs capping layer and the time of growth interruption and InAs layer thickness. The photoluminescence (PL) spectra showing the shift of the peak position reveals the tuning of the electronic states of the QD system. Enhanced uniformity of Quantum dots is observed judging from the decrease of full width at half maximum of FL. Injection InAs/GaAs quantum dot lasers have been fabricated and performed on various frequencies. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Electronic and vibrational Raman scattering in resonance with yellow luminescence transitions in GaN on sapphire substrate

We analyze low-temperature Raman and photoluminescence spectra of MBE-grown GaN layers on sapphire. Strong and sharp Raman peaks are observed in the low frequency region. These peaks, which are enhanced by excitation in resonance with yellow luminescence transitions, are attributed to electronic transitions related to shallow donor levels in hexagonal GaN. It is proposed that a low frequency Raman peak at 11.7 meV is caused by a pseudo-local vibration mode related to defects involved in yellow luminescence transitions. The dependence of the photoluminescence spectra on temperature gives additional information about the residual impurities in these GaN layers.

Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.