The concept of the intermediate band (IB) solar cells (SC) offers the promise of achieving 63% conversion efficiency devices. The effect of the type II band alignment in the quantum dot (QD) IB SCs on the above percentage is analyzed and the potential of the Ge/Si system for fabrication of the type II QD IB SC is discussed. Also, it is shown that the increase of the sunlight concentration leads to the rise of the potential barrier around QDs and the concentration of S x ≈ 700 can induce the ε L = 0.2 eV height barrier in the Ge/Si system, making this a significant result. Furthermore, the increase of the sunlight concentration leads to the separation of the quasi-Fermi levels from the confined states and also leads to the decrease of the recombination activity in QDs. The two-photon absorption in QDs increases rapidly and dominates over recombination at the moderate concentration. As the contributions of QDs to both the photo-and dark currents in the type II QD IB SC are evaluated it is shown that, compared to the conventional Si SCs, the type II Ge QD IB Si SCs can generate about 25% higher photocurrent and conversion efficiency.

Elxtron and L-n) difhction parrems uers [&en from four different N I , -~R~ alloys. uith x = 0 25.0.35.0 ?J and 0 SO. to Lnaehma thc cxtslcnw and shape of the diffuru tntens~ty. which gwes us mformamn about rtructurd Ruciu3iions A p ? d w rhapc of dlHuse scxtenq has o c m obsmcd at I O 0 md I IO ma their cquirdent posmons in the pmncms. thc shap of the uiffusr. mtcnsir> at [he IO0 position chvlgins sith PI content In the all0)s. The shape of the diffue mehit) at the 100 position ior th: I = 0 25 allo) IS rod.lAe. but thc shape 1s ncxly sphmcil for the I = 0 50 dlo) Thi \.raj diffuse scetenng intensities urn mezurcd from the I = 0.50 s m z l c -q s d allo) at room tempmure. m d the Wmen-Coulq shon-rmgc order p x m e t e n neIe determned aft<, mi.),mg thr. dan Thc corrc.mon length has been deduced to be aboJt 19 A from <,ttmang the i n r e r~e of In< full width at hall-mumum of the diffuse peak

A model of a quantum dot (QD) buried solar cell is described. The cell takes advantage of the generation of an additional photocurrent by a two-photon excitation of electrons from the valence band into the conduction band via the confined (intermediate) state. Since the intermediate states are active recombination centres suppressing the open-circuit voltage and the conversion efficiency either by increasing the dark-current or by arresting the quasi-Fermi level of mobile carriers, a barrier layer promoting the separation of the quasi-Fermi levels is built in around the QDs. Conditions for the separation of the quasi-Fermi levels and the activation of the two-photon generation of mobile carriers were found. Under these conditions the photocurrent and the conversion efficiency of the Ge QD buried Si solar cell exposed to concentrated sunlight must be approximately 25% larger than that of conventional Si solar cells.

Bistable semiconductor lasers have potential applications in future optical communication, optical switching, optical computing, and so on [I] Although gain saturation alone could account for the bistability, the inclusion of absorption saturation could make the bistability easier to occur [2]. As a result, multi-elecbode semiconductor lasers are usually used for optical bistability. In this work, we report that bistability exists in the semiconductor lasers without multiple sections. Using multiple quantum wells of different widths, both gain quenching and saturable absorption could occur in the same region for bistability The semiconductor lasers that exhibit optical bistability have four quantum wells with their widths 20& 33.4, 56& and l 2 5 G respectively, separated by 150 A Ab,%&barrier. An external-cavity configuration with broadband tunability was used for the bistability experiment. Different behaviors of bistability had heen discovered for different wavelengths. Fig 1 shows an L-I curve with obvious bistability. The details of experiments will be discussed in the presentation. 7 0 816nm 6 Fig 1 An L-I curve at lasing wavelength of 816 nm that exhibits hysteresis. Currenl(m.4) References: [I] Hitoshi Kawaguchi, IEEE J. Select. Topics Quantum [2] Ching-Ameaiq phone: (3742) 556383, Fax: (3742) 151087The resonant =tun of the excitation of surface ele3"apdic waves (SEWs), i.e. the r e s " dependence of the reflectivity on the incident radiation wavevedor component parallel to the interface (swhe), k, leads to the nonlinear phenomena arising and particularly optical biand multi-stability ~ppearance at relatively small nonlinearities. At such nonlinvinties the fieldinduced variation of SEW wavevectoi, K, becomes comparable with the width, lm(K), of the mentioned geometrical (angular) r e m " .In this paper the thwry of optical bi-and multistability at the excitation of TM-polarized SEWs via Kre~~chmann attenuated total reflection (Am) nchemc (glass prism-metal film-dielechic) in which the dielectric exhibits a relatively small one. or huo-photon resonant nonlinearity is presented. The system of equations describing the excitation of nonlinear SEWs is presented in eneral fom for arbitrq type of nonline& by means of SEW wavevector nonlinear term, 9, It is the Same form which in e m of cubic nonlinearity has ban presented in [I]. The value of K #' is determined via [2] : K" -K O I [~" ( i ) + i K , K , ' P~( 1 ) I . X P ( -K , z )~,where x is the SEW propagation direetion, z is the direction of perpendicular to metaldielectric intecfce, p"'. is the amplitude of medium nonlinear QolariZatiOn, K, is the linear term of SEW wmwector,L, = (K: -( m / c ) '~, ] ' ' . zd is the dielectric pemimvity ofnonlinear medium. In the case of one-photon resonance on the dependence of reflectivity on incident radiation intensity the hysteresis loop of aptkal bistability arises when the concenhalion of resonant putides exceeds the corresponding threshold. That threshold is the function of frequency and wwevectm mismatches ( o -m 2 ,...

We develop a means to reconstruct an input complex coherent scalar wavefield, given a through focal series (TFS) of three intensity images output from a two-dimensional (2D) linear shift-invariant optical imaging system with unknown aberrations. This blind phase retrieval technique unites two methods, namely (i) TFS phase retrieval and (ii) iterative blind deconvolution. The efficacy of our blind phase retrieval procedure has been demonstrated using simulated data, for a variety of Poisson noise levels.