We demonstrate the existence of an interfacial barrier in blocked impurity band (BIB) detectors using temperature-dependent dark current and corresponding theoretical calculations. Considering the effects of the interfacial barrier, the calculated photoresponse is in good agreement with the experimental results. A dual-excitation model, including the direct excitation over the full barrier and excitation to the band minimum with subsequent tunneling into the blocking layer, is proposed to quantitatively explain the observed photoresponse extension. A concept of extended-mode detection is developed to suggest the option for some selective photoresponse in the terahertz region and open the possibility of extending BIB photoresponse to lower frequency.

We report a 2D simulation of electrical and optical characteristics of green color InGaN/GaN multiple quantum well light-emitting diodes by APSYS software with a dot-in-well model. The In-rich quantum dot-like structure in InGaN/GaN multiple quantum wells has been considered in the LED experimental data analysis. Simulation results based on the quantum dot model are in better agreement with the experimental data than those based on the purely quantum well model, indicating that the quantum dot spontaneous emission and the non-equilibrium quantum transport play important roles in the InGaN/GaN multiple quantum well light-emitting diodes.

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We report our investigation on Piezoreflectance spectra (PZR) of a conventional InAs quantum dots (CVQD) and an InAs/InO.15GaO.85As dots-in-a-well (DWELL). A large red-shift of ground state QDO between two samples is attributed mainly to larger size of DWELL induced by the activated strained-driven decomposition. Both samples were grown by solid source molecular beam epitaxy (MBE) technology. Simplified growth sequence for Inas DWELL shows as following: where, InAs QDs was grown on a 2nm thick Ino.15Gao.85As layer and covered by another 6nm thick InO.15GaO.85As layer. The growth temperature is 5 10°C for Ino.15GaO.85As QW and InAs QDs, while 610°C for the rest layers of DWELL. Another InAs CVQD sample (only lack of the Ino.15Gao.85As layers)was grown under the same conditions directly on the GaAs matrix for comparison.The PzR spectra of two samples at room temperature and their best fitting curves have been shown in Fig. 1. The features originated from InAs DWELL (QDn, n=0, 1,2,) and the two features, CL1 and CL2, associated to the sandwiched WL+QW structure have been labeled in Fig. 1, respectively. These features have been identified with the PL spectra. As for InAs CVQD, two features (QDO and QD1) associated with the InAs dots, and WL from the InAs well formed by the InAs wetting layer and GaAs layer. The ground state QDO of DWELL and CVQD are observed at 1.072eV and 1.136eV, respectively. It is interesting to note that a larger red-shift of QD0 is observed about 64meV between DWELL and CVQD. The physical origins for the red-shifts can be attributed mainly to larger sizes of DWELL induced by the activated strained-driven decomposition.[1]: The calculations based on one-dimensional effective mass approximation and the band structure in the inset of Fig. 1 shows the real x value in InxGal, As layre is x=0. 136 in the sandwiched WL+QW structure, instead of nominal value x=0. 15.. There the missing of transfer and an accumulation at InAs DWELL [2], which lead to the increase of DWELL sizes. The AFM line-scan results indicate that the height and the lateral size of DWELL increase 50% and 15%, respectively, compared with that of CVQD. Generally, the increasing QDs sizes and the In atoms injection into DWELL will lead to the shrinkage of band gap as one observed in the PzR experiments [2]. .F Q0 n1 N Photon energy(eV) Figure 1. Upper panel shows the PL spectra of DWELL, insert shows the band structure of WL+QW in DWELL; nether panel gives the PzR spectra of the two samples at 300K. REFERENCES [1] F. Guffarth, R. Heitz, A. Schliwa, 0. Stier, N. N. Ledentsov, V. M. Ustinov, D. Bimberg , "strain engineering of InAs quantum dots", Phys. Rev. B vol.64, pp.085305, 2001. [2] V.

Multiple confined‐state transitions within surface quantum dots deposited on In0.35Ga0.65As template grown on GaAs (311)B substrate, as well as signals from all other relevant portions of the samples including buried QDs, In0.35Ga0.65As template, and GaAs‐related layers, at 77 K, were obtained in a piezomodulation reflectance spectroscopy (PzR) study. The measured transition energies were accurately determined using a Gaussian lineshape fit based on the reference of PL results. Four factors caused the large energy shift (larger than 400 meV) of confined states within SQDs compared to the buried QDs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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