Photonic molecules have been fabricated by coupling pairs of micrometer-sized semiconductor cavities via a narrow channel. The optical modes in these structures have been studied spectroscopically as a function of the coupling and the mode energies are compared to detailed calculations. These results provide a rich picture of photonic modes in these molecules. [S0031-9007(98)
InAs quantum-dot (QD) lasers were investigated in the temperature range 20-300 K and under hydrostatic pressure in the range of 0-12 kbar at room temperature. The results indicate that Auger recombination is very important in 1.3-m QD lasers at room temperature and it is, therefore, the possible cause of the relatively low characteristic temperature observed, of 0 = 41 K. In the 980-nm QD lasers where 0 = 110-130 K, radiative recombination dominates. The laser emission photon energy las increases linearly with pressure at 10.1 and 8.3 meV/kbar for 980 nm and 1.3m QD lasers, respectively. For the 980-nm QD lasers the threshold current increases with pressure at a rate proportional to the square of the photon energy 2 las . However, the threshold current of the 1.3m QD laser decreases by 26% over a 12-kbar pressure range. This demonstrates the presence of a nonradiative recombination contribution to the threshold current, which decreases with increasing pressure. The authors show that this nonradiative contribution is Auger recombination. The results are discussed in the framework of a theoretical model based on the electronic structure and radiative recombination calculations carried out using an 8 8 k p Hamiltonian.
The optical modes of chains of coupled micron sized semiconductor cavities have been studied using photoluminescence spectroscopy and detailed calculations. With an increasing number of cavities, the chains exhibit photon band gaps at several Brillouin zone boundaries. The sizes of the band gaps are shown to depend on the coupling between the microcavities and also on the order of the Brillouin zone involved. PACS numbers: 78.55.Cr, 42.70.Qs Systems which exhibit photon band gaps analogous to the band gaps in the electronic states of periodic solids have been the subject of intense investigations in the past decade [1][2][3]. In the photonic case, the forbidden energy gaps in the frequency spectrum result from a periodic modulation of the refractive index. These systems are called "photonic crystals" and calculations of their properties for a number of structures have been made [1,2,4]. They permit the coupling between photons and electronic excitations to be studied and controlled in powerful ways, including the introduction of highly localized defect modes in the band gaps.Experimentally, to date photonic crystals have been realized over several parts of the electromagnetic spectrum [5][6][7][8][9][10][11][12][13][14]. The near infrared and the visible range is particularly important for potential applications as well as for fundamental studies [15,16]. Photonic crystals could be used, for example, to obtain semiconductor lasers with zero, or low, threshold due to the possibility of suppressing the spontaneous emission by photonic energy gaps. Defect modes in band gaps are of interest in connection with waveguides for ultrasmall integration.Recently it has been shown that micron sized semiconductor resonator cavities exhibit sharp photonic resonances resulting from the strong optical confinement in all three directions [17][18][19]. The vertical confinement of the photon modes is effected by Bragg mirrors, and the lateral confinement is caused by etching of the cavity. In this way, strong photonic resonances are created in the cavities whose energies are controlled by the cavity size. These modes are analogous to the sharp electronic states of atoms or quantum dots.In the present work we have created a photonic band gap system for frequencies in the near infrared by putting together microcavities in chains. We are able to construct a system by adding individual building blocks ("photonic atoms") one by one. Angle-resolved photoluminescence spectroscopy is used to study the emergence of a photonic band structure: In chains formed from an increasing number of cavities we observe a transition from discrete atomiclike modes to the photonic band structure of a solid with band gaps at several Brillouin zone boundaries. We are able to modify the modulation of the refractive index by varying the coupling between the cavities, and the energy gaps are found to increase with increasing modulation. We show that the experimental results are in quantitative agreement with numerical calculations of the photonic band struct...
We describe a theoretical model for the linear optical gain properties of a quantum wire assembly and compare it to the well known case of a quantum dot assembly. We also present a technique to analyze the gain of an optical amplifier using bias dependent room temperature amplified spontaneous emission spectra. Employing this procedure in conjunction with the theoretical gain model, we demonstrate that InAs/InP quantum dash structures have quantum-wire-like characteristics. The procedure was used to extract the net gain coefficient, the differential gain, and the relative current component contributing to radiative recombination.
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