Volume 79, Issue 20, 12 November 2001
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
Coupled InP quantum-dot InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructure diode laser operation79(2001); http://dx.doi.org/10.1063/1.1416158View Description Hide Description
Data are presented showing that a quantum-dot (QD)heterostructurediode, with an auxiliary ∼20 Å InGaP quantum well(QW) coupled via an In(AlGa)P barrier (∼20 Å) to the single layer of QDs to aid carrier collection, has a steeper current–voltage characteristic than the case of a similar diode with no auxiliary QW. The diode is capable of 300 K visible-spectrum QDlaser operation, while the single-layer InP QDdiode (single QD layer) saturates at low current (≲1 mA) and does not exhibit stimulated emission.
79(2001); http://dx.doi.org/10.1063/1.1418264View Description Hide Description
Absorption spectra obtained from spark-processed Si (sp-Si) utilizing differential reflectometry yield a series of closely spaced energy levels, as expected for amorphous materials, which reside between 1.7 and 2.8 eV. Further, a broad absorption band is observed between about 3.2 and about 6.2 eV. A HeCd laser pumps electrons from the ground state into this absorption band. The blue and green photoluminescence peaks of sp-Si are interpreted as originating from emission energy levels at 3.22 and 2.36 eV into which the electrons revert from the just mentioned absorption band by nonradiative transitions. In contrast, pumping with an argon ion laser provides only enough energy to excite the electrons from the ground state into the above mentioned, closely spaced, lower absorption bands and thus causes only a 1.9 eV (red) radiation.
Mid-infrared photonic-crystal distributed-feedback laser with enhanced spectral purity and beam quality79(2001); http://dx.doi.org/10.1063/1.1418445View Description Hide Description
We report a photonic-crystal distributed-feedback (PCDFB) laser with an antimonide type-II “W” active region. Optical lithography and dry etching were used to pattern the two-dimensional rectangular lattice with a second-order grating tilted by 20° relative to the facet normal. For pulsed optical pumping, the emission line centered on is considerably narrower (7–10 nm) than for Fabry-Pérot and angled-grating DFB (α-DFB) lasers fabricated from the same wafer. The PCDFB beam quality is also substantially enhanced, e.g., by a factor of 5 compared with the α-DFB at a pump-stripe width of 200 μm.
79(2001); http://dx.doi.org/10.1063/1.1415410View Description Hide Description
By using a perturbative approach, we propose a simple, systematic, and efficient method to engineer acoustic band gaps. A gap can be enlarged or reduced by altering the microstructure according to the field-energy distributions of the Bloch states at the band edges as well as their derivatives. Due to the structure of the acoustic waveequation, the engineering of acoustic band gaps is much more efficient than that of photonic band gaps. The validity of the proposed method is supported by multiple-scattering calculations. Our method makes the acoustic band gap “designable.”
Surface photovoltage spectroscopy characterization of a GaAs/GaAlAs vertical-cavity-surface-emitting-laser structure: Angle dependence79(2001); http://dx.doi.org/10.1063/1.1418027View Description Hide Description
An angle-dependent surface photovoltage spectroscopy (SPS) study has been performed at room temperature on a GaAs/GaAlAs-based vertical-cavity-surface-emitting-laser (VCSEL) structure emitting at a wavelength near 850 nm. For comparison purposes, we have also measured the angle-dependent reflectance (R). The surface photovoltage spectra exhibit both the fundamental conduction to heavy-hole (1C–1H) excitonic transition and cavity mode plus additional interference features related to the properties of the mirror stacks, whereas in the R spectra only the cavity mode and interference features are clearly visible. The energy position of the excitonic feature is not dependent on the angle of incidence, in contrast to that of the cavity mode, whose angular dependence can be fitted with a simple model. This study demonstrates the considerable potential of angle-dependent SPS for the contactless and nondestructive characterization of VCSEL structures at room temperature.