摘要:

Surface photovoltage spectroscopy (SPS) has been employed to monitor optical transitions in quantum well and superlattice structures at room temperature. Excellent agreement is found between theoretical predictions of heavy hole and electron energy level positions and the observed transitions. The results show that using this technique, the complete band diagram of the quantum structure may be constructed. SPS emerges as a powerful tool capable of monitoring optical transitions above the lowest one in a simple to interpret, contactless, and nondestructive way. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116217

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A voltage controlled, multilayer electro‐optic structure is proposed. It is constructed from repeated Schottky‐like modules, which consist of layers of semiconductor‐dielectric‐semiconductor. The device reflectivity, in the range of incidence angles corresponding to surface plasmon excitation, is determined by the combined thickness and permittivity of the semiconductor space charge regions of all modules. A structure consisting of many modules allows for a large effective thickness of the voltage controlled space charge region which yields a high reflectivity modulation. Calculations show that fast (response time ∼ 10−10s) and low‐voltage structures with reflectivity modulation depth of more than 80% can be constructed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116218

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Radially and azimuthally oriented liquid crystal (LC) alignment patterns, which are hard to achieve by conventional LC alignment techniques, have been realized by exposure of polyimide surfaces to linearly polarized ultraviolet radiation. These surfaces can be used to realize some special LC configurations which are useful for LC basic research and applications. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116219

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The measured polarization hysteresis loop for a Z‐cut LiTaO3crystal was found to be asymmetric about the field axis indicating the presence of an in‐built internal field in the crystal of 5 kV/mm in the direction of the original polarization in the virgin crystal. Upon polarization reversal under electric field, the internal field tends to realign along the new polarization direction. Systematic time–temperature dependence of this realignment process was carried out. At room temperature, this realignment process was incomplete even after many days, while above 200 °C, the recovery process takes less than 30 s. Conductivity measurements also indicate an exponential increase in the dc conductivity of the sample above 200 °C with an activation energy of 1.55 eV. Further experiments related to the behavior of the internal field with change in sample thickness and surface removal revealed that the internal field is a volume effect. Possible origins of this field based on point defect chemistry of the crystal are discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116220

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Continuous wavelength tuning of 15 nm was achieved micro‐electromechanically in an InGaAs/AlGaAs vertical‐cavity surface‐emitting laser operating near 960 nm. The device utilizes a micromachined deformable‐membrane top mirror suspended by an air gap above ap‐i‐ndiode quantum well active region and bottom mirror. Applied membrane‐substrate bias produces an electrostatic force which reduces the air gap thickness and therefore tunes the lasing wavelength. Typical tuning bias ranged between 15 and 23 V, and the minimum threshold current was 35 mA for pulsed room‐temperature operation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116221

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Most polymer electroluminescent devices to date are represented as tunnel diodes and operate under direct‐current (dc) driving field. Here we report the fabrication of symmetrically configured alternating‐current (ac) light‐emitting (SCALE) devices based on conjugated polymers. The new devices consist of an emissive polymer layer sandwiched between two redox polymer layers. This configuration enables the SCALE devices to work under both forward and reverse dc bias as well as in ac modes. The nearly ohmic electrode/redox polymer contacts improve the charge injection efficiency significantly and make the SCALE device operation insensitive to electrode work functions. Symmetric operation supports the key role of redox polymer/emissive polymer interface states. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116222

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An emission band has been observed near 820 nm in a series of KTiOPO4crystals grown by the flux technique. Photoluminescence spectra were obtained at room temperature using an excitation wavelength of 457 nm and a power density of 1.9 kW/cm2. When a crystal was held for 1 h in air at 1000 °C, the intensity of the emission increased by two orders of magnitude. Micro‐Raman spectra taken at the same location as the photoluminescence revealed that the high‐temperature anneal caused significant decomposition at the KTiOPO4surface. Potassium, phosphorus, and oxygen evolved from the surface and left TiO2(anatase). The increase in emission correlated with the amount of anatase created. This enhanced near‐infrared emission arises from Ti3+ions which are formed by reduction in the TiO2surface layer during the decomposition process. Since the 820‐nm emission is observed in as‐grown crystals, our data suggest that some reduced TiO2(rutile or anatase) is formed in the bulk of KTiOPO4crystals during growth. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116223

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We investigate the effects of UV exposure on the growth of optical fiber rocking filters written in hydrogen‐loaded germanosilicate elliptical core fibers. We find that with increasing exposure, the rocking angle (induced birefringence) increases rapidly then begins to decrease, eventually erasing completely. With further exposure, the rocking angle is seen to increase again, reaching values of 3.5°. This corresponds to a photoinduced birefringence almost four times larger than previously recorded in optical fiber rocking filters. Furthermore, we show that at high UV fluences, the direction of rotation of the birefringent axes is opposite to that at low fluences. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116224

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ion drag refers to Coulomb momentum transfer collisions between a directed flux of charged particles and a second charged species. It is an important force in determining the motion of negatively charged dust particles in plasma processing reactors. The same ion drag mechanism acts between the directed flux of positive ions moving towards the boundaries of a plasma etching reactor and negative ions being accelerated by electrostatic forces towards the center of the plasma. In this letter, we discuss the parameter space for inductively coupled plasma etching reactors in which ion drag forces on negative ions influence their transport using results from a two‐dimensional plasma equipment model. We find that ion drag forces on negative ions are important at high plasma densities and low ion temperatures. Under these conditions, the large positive ion flux, coupled with a large Coulomb cross section, creates an ion drag force which may dominate the electrostatic forces on negative ions. The end result is that negative ions may accumulate near the sheath edge. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116225

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have carried out a transmission electron microscopy based study of AlGaAs–Al(oxide) heterolayers created by lateral sidewall wet oxidation and identify the oxide phase formed as a consequence of the oxidation of AlAs to be &ggr;‐Al2O3, with the cubic Fd 3mstructure. The oxide‐semiconductor interface is weak and porous, possibly due to the high stress loads developed during oxidation, and we propose that the fast oxidation rates are a consequence of reactants transported to the oxidation front along the porous interface. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116226

出版商:AIP    

年代:1996

数据来源: AIP