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  • 1
    Digitale Medien
    Digitale Medien
    CdS/CdSe intrinsic Stark superlattices (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 907-915 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Strained layer superlattices of wurtzite CdS/CdSe have been grown on (111)A GaAs substrates by metalorganic chemical vapor deposition and their optical properties studied by photoluminescence spectroscopy. It is shown that the superlattice layers contain giant strain-induced piezoelectric fields exceeding 2×108 V m−1. These fields are similar to those reported for (111) orientated III–V superlattices, but an order of magnitude greater. The recombination energies from a series of samples provide evidence for a type II conduction band offset of 0.23±0.10 eV (the electron wells being in the CdS), with the band structure heavily modified by the internal electric fields. In addition, the photoluminescence peak emission energy shows a strong dependence on the excitation power. This is interpreted as further evidence for the effect of internal fields. We conclude that this system shows new effects not previously observed in II–VI compound superlattices. The large band-gap tunability and the space-charge effects offer possibilities for all-optical switching devices in the 700–1300-nm region of the spectrum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351312
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  • 2
    Digitale Medien
    Digitale Medien
    Excimer laser induced diffusion in magnetic semiconductor quantum wells (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1373-1379 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Studies of pulsed laser annealing (PLA) of CdTe/CdMnTe quantum well structures are made in order to examine depth dependent effects in laser irradiated semiconductors. Since diffusion coefficients are strongly dependent on the temperature, depth resolution is achieved because the diffusion of Mn from the barriers into the quantum wells is depth dependent. Multiple quantum well (MQW) structures of CdTe/CdMnTe were annealed with single pulses from an XeCl laser at 308 nm. At a threshold of 90 mJ cm−2 two new emission bands are observed that are attributed to the diffusion of Mn from barrier layers to QWs. The diffusion associated with these bands, measured as the integrated product of the diffusion constant and time, is found to be 300 and 30 Å2. Calculations of the temperature, reached within the surface following PLA, using an analytical solution of the heat diffusion equation coupled with known high temperature diffusion coefficients predict the diffusion to decrease by one order of magnitude within one period at the top of the MQW stack. It is suggested that at the threshold surface melting occurs and that these emission bands arise from the QWs immediately beneath the melt front. The diffusion of Mn ions into the QWs is confirmed by magneto-optical data. A further emission band occurs at this same threshold with a Mn concentration above that of the concentration in the barrier layers of the MQW stack. This emission is attributed tentatively to the segregation of the Mn ion within the molten region following recrystallization. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.373826
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  • 3
    Digitale Medien
    Digitale Medien
    Independent contacts to a double-electron gas using mesoscopic surface gates (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4036-4038 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We demonstrate how two two-dimensional electron gases can be independently contacted using only surface gates defined by electron-beam lithography: macroscopic bar gates to contact the lower layer, and mesoscopic split gates to contact the upper layer. When the technique is applied to a sample consisting of two 150 Å GaAs wells separated by 300 Å Al0.33Ga0.67As barrier, there is more than 30 MΩ isolation at 5 K for interlayer voltages up to ±30 mV; the interlayer isolation operates up to 30 K. The independent contacts are used for a preliminary investigation of two parallel one-dimensional quantum wires. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372451
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  • 4
    Digitale Medien
    Digitale Medien
    Measurement of interdiffusion in II–VI quantum-well structures using optical methods (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1895-1897 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The extent of interdiffusion in Cd1−xMnxTe/CdTe quantum-well structures grown by molecular-beam epitaxy was monitored by photoluminescence and photoluminescence excitation spectra. Thermal annealing of as-grown and ion-implanted structures in over pressures of cadmium (or tellurium) provide clear evidence that diffusion is controlled by cation vacancies and are consistent with a strong dependence of the interdiffusion coefficient on the vacancy concentration. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361092
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  • 5
    Digitale Medien
    Digitale Medien
    Control of nitrogen incorporation in ZnTe:N grown by molecular-beam epitaxy using Ar dilution in a N plasma source (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5214-5217 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The use of Ar dilution in a N plasma source has been used to achieve control of both electrical and optical properties of p-type ZnTe:N grown by molecular-beam epitaxy. Photoluminescence data are presented that show the transition from "pure'' ZnTe emission to that indicative of heavily N-doped ZnTe. A new principal bound-exciton line associated with N impurities is observed at 2.3685 eV. An anomalous red shift in the corresponding donor-acceptor pair peak energy with increasing N concentration is observed at high N concentration and is attributed to the effects of N impurity banding. Trends in p-type conductivity confirmed the ability to control hole concentrations using Ar dilution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357190
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  • 6
    Digitale Medien
    Digitale Medien
    Photoluminescence and p-type conductivity in CdTe:N grown by molecular beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5423-5428 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An rf nitrogen (N) plasma source has been used to achieve p-type conductivity in molecular beam epitaxy CdTe layers grown with a Cd overpressure. Photoluminescence and secondary ion mass spectrometry measurements have confirmed the incorporation of the N species, and evidence for the resulting p-type conductivity has been obtained using capacitance-voltage and current-voltage techniques. Net hole concentrations as high as 2×1017 cm−3 have so far been achieved, which contrasts with the normally n-type nature of our undoped CdTe layers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357197
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  • 7
    Digitale Medien
    Digitale Medien
    On the lack of influence of disorder in Cr3+-doped LiSr0.8Ca0.2AlF6 (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2232-2234 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optical and electron spin resonance spectroscopies have been used to investigate the thermal stability of lasers based on Cr3+:LiSr0.8Ca0.2AlF6, a material in which the onset of critically inhibiting nonradiative decay at temperatures below 300 K might be expected based on results from other Cr3+-activated disordered gain media. The influence of disorder on the Cr3+ environment is shown to be very small in LiSr0.8Ca0.2AlF6 so that the 4T2→4A2 fluorescence transition is not broadened relative to that in LiSrAlF6 and the onset of significant nonradiative decay is also held above room temperature. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121330
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  • 8
    Digitale Medien
    Digitale Medien
    Bias dependence of instability mechanisms in amorphous silicon thin-film transistors (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1242-1244 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the bias dependence of the threshold voltage shift in a series of amorphous silicon-silicon nitride thin-film transistors, where the composition of the nitride is varied. There are two distinct instability mechanisms: a slow increase in the density of metastable fast states and charge trapping in slow states. State creation dominates at low fields and charge trapping dominates at higher fields. The state creation is found to be independent of the nitride composition, whereas the charge trapping depends strongly on the nitride composition. This is taken as good evidence that state creation takes place in the hydrogenated amorphous silicon (a-Si:H) layer, whereas the charge trapping takes place in the a-SiN:H. The metastable states are suggested to be Si dangling bonds in the a-Si:H, and the state creation process similar to the Staebler–Wronski effect. The confirmation of state creation in a thin-film transistor means that states can be created simply by populating conduction-band states in the undoped material. The slow states are also thought to be Si dangling bonds, but located in the silicon nitride matrix.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.98692
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  • 9
    Digitale Medien
    Digitale Medien
    Anderson localization and Monte Carlo simulation of vertical transport in disordered finite superlattices (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4378-4383 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects on the carrier wave functions of introducing monolayer disorder at the heterojunction interfaces of an undoped superlattice are elucidated. In particular the rate and extent of the resulting localization is quantified by means of an entity C, which is the joint probability of finding two carriers in the same region of space. Evaluating the latter for all states in the miniband provides clear evidence for the existence of a mobility edge in finite two-dimensional structures. Using the entity C as the basis for a semiclassical evaluation of carrier transport, it is shown that the experimentally observed activated transport can be accounted for in terms of the excitation of carriers from the localized states at the bottom of the miniband into the more extended midband miniband states. Comparison of the theoretical results with the experimental results given [Chen et al., J. Cryst. Growth 159, 1066 (1996)], enables conclusions to be drawn concerning the mechanism of activated carrier transport in doped superlattice systems. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.366248
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  • 10
    Digitale Medien
    Digitale Medien
    Spectroscopic evidence for different laser gain mechanisms in optically pumped ZnCdS/ZnS quantum well structures (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5621-5625 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The role of biexcitons has been studied in two optically pumped quantum well (QW) structures of Zn1−xCdxS/ZnS, one with 18% Cd concentration and the other with 3% in the wells. For the x=18% QW structure, high excitation photoluminescence and stimulated emission indicate that the laser gain mechanism involves biexcitons. For the x=3% QWs, even though biexcitons are clearly observed in the spontaneous emission, they are not responsible for laser gain in this structure. Instead exciton–exciton scattering may be the more likely mechanism responsible for laser gain close to threshold, while at higher densities an estimate of the carrier density indicates an electron–hole plasma as the likely source of optical gain. The different mechanisms in the two cases can, very likely, be attributed to one of differing degrees of localization both within the QW and at alloy fluctuations. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368609
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