Michael A. Haase

Organic semiconductor RFID transponders

We present pentacene-based radio frequency identification (RFID) transponder circuitry, patterned entirely using flexible shadow-masks, and operating at RF frequencies greater than 1 MHz. The circuits, fabricated on glass substrates, were powered using near-field inductive coupling, and designed for operation without a rectification stage. 1-bit transponders made using this approach operated at RF frequencies of 125 kHz (a common RFID frequency), and well above 1 MHz, and exhibited sufficient amplitude modulation of the absorbed RF to be detected externally with peak-detection demodulation.

Universal coupling between metal-clad waveguides and optical ring resonators

We demonstrate excitation of whispering gallery modes in optical ring resonators using a gold-clad pedestal planar waveguide structure. The gold-clad structure provides a strong evanescent field for light-coupling into the resonator while enabling low transmission loss throughout much of the visible and near-infrared region. This is advantageous compared to the previously demonstrated anti-resonant reflecting optical waveguide (ARROW) structure, which can only transmit a narrow wavelength band. We show that the height of the pedestal waveguide can be designed to optimize the coupling conditions for the ring resonator. This technology enhances the practicality of optical ring resonators for sensing devices, laser systems, and many other important applications.

Effects of strain on defect structure in II-VI green color converters

State-of-the-art green emission efficiency has been achieved with light-emitting diodes incorporating CdMgZnSe color-converting quantum well heterostructures, although dark line defects (DLDs) limit the device reliability. We have determined that misfit strain plays an important role in the formation of extended stacking faults (SFs) and DLDs in II-VI green converters. Even small strain causes SFs to extend to accommodate misfit strain and extended SFs further give rise to DLDs when they intersect active regions. Detailed strain relaxation mechanisms for both tensile and compressive strain have been investigated, which may apply for other semiconductor heterostructures with an fcc lattice. Careful control of the layer strain via close lattice matching prevents the extension of SFs and leads to DLD-free converters.

High efficiency green LEDs using II-VI color converters

II-VI semiconductors can exhibit strong photoluminescence throughout the visible spectrum and are excellent candidates for filling the so-called green gap. We report on the performance of green color-converted LEDs fabricated by bonding CdMgZnSe multiple quantum well structures to high-efficiency blue-emitting GaInN LEDs. A device efficacy of 181 lm/W at 537 nm (dominant) is measured under room temperature, 350 mA/mm2 quasi-cw conditions, more than twice as efficient as typical commercial green LEDs today. The thermal roll-off is shown to be comparable to that of typical green GaInN LEDs. Finally, the implications of the availability of high-efficiency, narrow-band, green and yellow emitters in display applications will be discussed.

Pentacene based RFID transponder circuitry

In this paper, we present a pentacene-based eight-bit radio frequency identification (RFID) transponder circuit. The circuits are patterned entirely with polymeric shadow masks and operate at carrier frequencies greater than 1 MHz. The thin film integrated circuits were fabricated using methods previously described (P.F. Baude et al., Appl. Phys. Lett., vol.82, p.3964, 2003). In the work reported here, we use an ac powering approach to power the logic and amplitude modulation circuitry. A description of the RFID circuit is given, along with details of the reader.

Coulomb enhancement CdZnSe single quantum well lasers

Data showing the dependence of lasing wavelength on cavity length for CdZnSe single quantum well, buried ridgeguide lasers is presented. The `slope of the data is opposite in sign to the slope calculated from conventional theory which includes carrier scattering and bandgap renormalization. The calculated slope with Coulomb enhancement included in the model has the correct sign and the correct magnitude to within 30%. Using the Coulomb enhanced model, the key spectral features reported as evidence for an excitonic gain mechanism in room temperature CdZnSe quantum well lasers are reproduced.

Enhanced efficiency of CdMgZnSe down-converted light emitting diodes using light extraction features fabricated by laser-speckle lithography

We report a method of making a wavelength converted, light-emitting diode (LED) having light extraction features based on coherent speckle patterns. These patterns have random feature size, random feature distribution, and random feature shape. The features were produced using a maskless lithography process based on exposing photoresist with a laser-induced coherent optical speckle pattern. A wet chemical etching process was then used to transfer the resist pattern into the underlying surface of the semiconductor wavelength converter layer. The external quantum efficiency of a wavelength converter with emitting surfaces having such extraction features showed a twofold increase compared to a wavelength converter without extraction features. While demonstrated here using semiconductor wavelength converters, this approach could also be applied to light extraction in conventional LED structures.

Low-Cost Displays—Semiconductor and Lithographic Performance Requirements

The field of low-cost flexible displays has attracted an enormous amount of interest in the past few years. This paper analyzes the challenges associated with designing a backplane for an electrophoretic front plane and develops a general model which relates semiconductor and lithographic performance metrics to display qualities such as speed, uniformity, and resolution. Specific examples are given for all ink-jet printed displays as well as for partially or all photolithographically patterned displays.

II-VI index-guided lasers for optical recording

We have demonstrated the feasibility of reading a high density Digital Versatile Disc using a green ZnSe based laser as the light source. In order to achieve this, high quality optical and electrical properties are required from the laser. We fabricated index-guided lasers to produce a single mode gausian optical beam having 7 micrometers of astigmatism. Operating electrical and optical parameters were measured and compare well with currently available semiconductor lasers for optical storage systems. The read- out experiment shows the favorable noise characteristics of ZnSe based lasers.

Gain-current relation in CdZnSe single quantum well lasers: modeling and experiment

Optical gain and spontaneous emission spectra are calculated for CdZnSe/ZnSSe single quantum well (QW) structures at room temperature with various many-body effects taken into account. It is found that Coulomb enhancement has a large effect on the gain-current relation derived from these spectra. When Coulomb enhancement is ignored, values of threshold current at various cavity lengths are overestimated by about 40 to 50% compared with the measured threshold currents. Good agreement with experiment is reached when Coulomb enhancement is included in the calculation.