Bernard L. Weiss

Low-loss planar optical waveguides fabricated in SIMOX material

Planar optical waveguides have been formed in SIMOX structures, and the effect of the thickness of the buried oxide layer on propagation loss hs been studied. Waveguides with a guiding layer thickness of approximately 6 mu m have been measured, and the lowest loss, which is on the order of that of pure silicon, was observed for a buried oxide thickness of 0.4 mu m, at a measurement wavelength of 1.523 mu m.<<ETX>>

Effects of interdiffusion on the sub‐band‐edge structure of In0.53Ga0.47As/InP single quantum wells

The disordering of In0.53Ga0.47As/InP single quantum wells has been studied using an error function distribution to model the compositional profile after interdiffusion. When considering interdiffusion on the group‐III sublattice only, a large strain buildup results during the early stages of disordering. Details are presented showing how this interdiffusion and the effects of strain lead to an interesting carrier confinement profile which differs from that of disordered AlGaAs/GaAs and InGaAs/GaAs quantum‐well structures. An abrupt confinement profile is maintained even after significant interdiffusion, with a well width equal to that of the as‐grown quantum well. The combined effects of strain with the unstrained band‐gap profile results in a potential buildup in the barrier near the interface, while it gives rise to two ‘‘miniwells’’ inside the potential wells. The sub‐band‐edge structure shows that the potential buildup can result in quasibound subband states, while the heavy‐hole well can support the ground state within the miniwells. In contrast, when identical interdiffusion on both group‐III and group‐V sublattices is considered, the structure remains lattice matched, the confinement profile changes to that of a graded profile, and the ground‐state transition energy shifts to shorter wavelengths.

Modal propagation within MQW waveguides

The propagation of TE modes and TM modes within planar multiquantum waveguides with large numbers of wells and barriers is shown to exhibit markedly different behavior for the two polarization states. The solutions for these two modes are developed for an arbitrary number of N barriers, and zero- and first-order approximations in powers of 1/N are calculated for quantities of physical interest. A very high geometric birefringence is demonstrated. >

Analysis of Franz-Keldysh oscillations in photoreflectance spectra of a AlGaAs/GaAs single-quantum well structure

Experimental results are presented for the physical origins of room‐temperature photoreflectance features of a AlGaAs/GaAs single‐quantum well structure. The spectra exhibit well‐defined Franz–Keldysh oscillations which overlap with photoreflectance features due to the quantum well and complicate the determination of the energies of the transitions within the quantum well. The origin of the Franz–Keldysh oscillations are determined using wet chemical etching to selectively remove grown layers down to the substrate. The resulting spectra are presented as a function of etch depth which allows the magnitude of the built‐in electric fields to be determined and reveals the location within the quantum well structure where the Franz–Keldysh oscillations originate.

Birefringent properties of GaAlAs multiple quantum well planar optical waveguides

Planar GaAlAs optical waveguides in which the waveguide core region is composed of multiple quantum wells are considered. Calculations of optical waveguide dispersion are performed to determine variations in effective refractive indexes for TE and TM modes and in the mode birefringence for large ranges of total waveguide thickness, number, and refractive index of well and barrier layers, and the ratio of well and barrier layer thickness. Ranges of these parameters which yield optical waveguides having unusually high birefringence and optical waveguides supporting single polarization planar propagation only are identified. >

Reactive ion etching of quartz and Pyrex for microelectronic applications

The reactive ion etching of quartz and Pyrex substrates was carried out using CF4/Ar and CF4/O2 gas mixtures in a combined radio frequency (rf)/microwave (μw) plasma. It was observed that the etch rate and the surface morphology of the etched regions depended on the gas mixture (CF4/Ar or CF4/O2), the relative concentration of CF4 in the gas mixture, the rf power (and the associated self-induced bias) and microwave power. An etch rate of 95 nm/min for quartz was achieved. For samples covered with a thin metal layer, ex situ high resolution scanning electron microscopy and atomic force microscopy imaging indicated that, during etching, surface roughness is produced on the surface beneath the thin metallic mask. Near vertical sidewalls with a taper angle greater than 80° and smooth etched surfaces at the nanometric scale were fabricated by carefully controlling the etching parameters and the masking technique. A simulation of the electrostatic field distribution was carried out to understand the etching pro...

Quantum‐confined Stark effect in interdiffused AlGaAs/GaAs quantum well

The quantum‐confined Stark effect is analyzed in an interdiffused Al0.3Ga0.7As/GaAs single quantum well (QW) with an as‐grown well width of 100 A, where the confinement profile is modeled by an error function. Results indicate a twofold enhancement of the Stark shift for the interdiffused quantum well over that of the square quantum well for a 50 kV/cm applied field. The fundamental exciton absorption peak also shows a much larger reduction with increasing applied field in the more extensively interdiffused QW. These characteristics may be used to realize optical modulators with higher on/off ratios and lower drive voltages.

Micromachining of three-dimensional GaAs membrane structures using high-energy nitrogen implantation

In this paper we present an alternative technology for micromachining gallium arsenide (GaAs) using deep ion implantation. Energetic nitrogen ions at 630 keV and 4 MeV have been used to implant deeply into an n-type GaAs substrate with doses of 2 x 10(14) and I x 10(15) cm(-2). After annealing at 600 degreesC, the nitrogen implanted n-GaAs top layer was converted to semi-insulating GaAs with a thickness of I mum for 630 keV and 2.5 mum for 4 MeV nitrogen ions. A pulsed electrochemical etching process has been developed to selectively remove n-GaAs and to leave the top patterned semi-insulating GaAs layer as a mechanical membrane structure. Various GaAs microstructures, such as cross-bridge, coiled and corrugated membranes, have been successfully fabricated using this micromachining technology.

Polarization dependent refractive index of an interdiffusion induced AlGaAs/GaAs quantum well

The polarization dependent refractive index, nR, at room temperature is calculated for interdiffusion‐induced Al0.3Ga0.7As/GaAs single quantum well (QW) structures for the wavelength range 0.75–2 μm. The confinement profile is modeled by an error function and nR is determined using the real and imaginary parts of the dielectric function, including contributions from the Γ, X, and L Brillouin zones. Results show that at longer wavelengths nR decreases with increasing interdiffusion, which normally provides a positive index step with respect to a less interdiffused QW. For shorter wavelengths (around the QW band edge), the wavelength range for a positive refractive index step increases as the extent of disordering between two interdiffused QWs is increasing.

The characteristics of high-resistance layers produced in n-GaAs using MeV-nitrogen implantation for three-dimensional structuring

The radiation damage introduced in n-GaAs by 4-MeV N+ implantation at a dose of 1×1015 cm−2 has been analyzed using micro-Raman spectroscopy. Implantation followed by annealing at 600 °C was found to produce a strongly compensated near-surface layer possessing a high crystalline quality. At the same time a pronounced disorder was found underneath the high-resistance layer which enables the fabrication of 2.5-μm thick free-standing membranes using selective electrochemical etching techniques.