Mark L. Biermann

Design and analysis of a diffraction-limited cat's-eye retroreflector

We describe a design for a modified, cats-eye retroreflector. The design is catadioptric, containing a single concave mirror and several lenses. This retroreflector design exhibits a unique combination of performance characteristics. It is diffraction limited over a large field angle while operating with a large aperture and numerical aperture. There is little vignetting of the optical beam, even at large field angles, providing good light return at all angles of incidence. It brings the light beam to a focus and allows access to the light near the focal plane, thus decoupling the size of the aperture from the size of devices used with the retroreflector. This final feature makes the design appealing for use with spatial light modulators, or other optical or electro-optical components.

Spectroscopic method of strain analysis in semiconductor quantum-well devices

The modification of the electronic bandstructure in a semiconductor, quantum well due to an induced strain is well known. Recently, we have developed a generalized, spectroscopic-based technique for analyzing the strain condition within devices based on quantum wells. This approach couples experimental data describing interband transition energies within strained, quantum-well devices with a rigorous theoretical description of the quantum-well bandstructure. The theoretical formalism is described, and various important theoretical predictions necessary in the application of this method are given. The accuracy of the theoretical model used in this approach is critical to its success, and it is therefore necessary to ensure the validity of the theoretical formalism as applied to quantum wells under a variety of strain conditions. We show the good agreement between theory and experiment for a number of known strain conditions within quantum wells and quantum-well devices. This agreement indicates the validit...

Quantitative strain analysis in AlGaAs-based devices

We present a strategy for quantitative spectroscopic analysis of packaging-induced strain using both finite element analysis and band-structure calculations. This approach holds for a wide class of AlGaAs-based, and related, devices, among them high-power “cm-bars.” The influence on the results of particular device structure properties, such as intrinsic strain and quantum-well geometry, is analyzed. We compare theoretical results based on a unaxial stress model with photocurrent data obtained from an externally strained cm-bar, and obtain better agreement than from alternative strain models. The general approach is also applicable to the analysis of all data that refer to changes of the electronic band structure, such as absorption and photoluminescence.

Device deformation during low-frequency pulsed operation of high-power diode bars

Thermal tuning rates of single emitters in “cm-bar” high-power diode laser arrays are analyzed. We find these tuning rates to consist of purely thermal and mechanical pressure contributions, of −0.48 and −0.08 meV(K)−1, respectively. We estimate the mechanical deformation such a device experiences during pulsed operation to be 0.07%, and then apply an adequate external force to single segments of cm bars. These single segments model the central emitters within the array. Effects that arise due to gradual aging, such as nonequilibrium carrier lifetime decrease, sheet carrier concentration increase, and defect concentration rise are monitored and analyzed over up to 2×106 deformation cycles. These experiments provide the basis for a type of accelerated aging experiment for device testing, especially of devices designed for low-frequency pulsed operation.

Enhanced optical polarization anisotropy in quantum wells under anisotropic tensile strain

Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited in optoelectronic devices such as modulators. A theoretical model shows that the behavior of the polarization anisotropy with increasing strain anisotropy is radically different for quantum wells under anisotropic tensile and compressive strains of equal magnitude. This strikingly different behavior arises from the different valence-subband mixing that occurs in the cases of anisotropic tensile and compressive strain. Specifically, the mixing of the first heavy- and light-hole subbands that occurs only under anisotropic tensile strain is central to the polarization anisotropy.

Laterally patterned band structure in micromachined semiconductors

We demonstrate that micromachining lattice-matched InGaAs quantum wells grown on (001) InP with strained barriers produces precise laterally patterned modifications to the semiconductor band structure. The light-hole and heavy-hole excitonic transitions are mixed and differentially shifted by the micromachining, inducing a surface-normal optical anisotropy characterized by a peak birefringence of Δn=0.028. The measured optical properties agree with calculations based on finite-element models of the strain combined with an eight-band k⋅p model that includes deformation potentials. This technique may find applications in fields such as surface-normal polarization modulators, quasi-phase matching, and optically-acitve piezoelectric materials.

Optical approach for determining strain anisotropy in quantum wells

Anisotropic in-plane strain arises in quantum-well systems by design or unintentionally. We propose two methods of measuring the in-plane strain anisotropy based on the optical polarization anisotropy that arises with anisotropic in-plane strain. One method uses purely optical means to determine the strain anisotropy in quantum wells under a compressive strain that is spatially varying. A second approach, applicable to quantum wells under tensile strain or with strain that does not vary with position, requires the application of a uniaxial in-plane stress. Although the second method is experimentally more difficult, it allows analysis of systems that would otherwise be inaccessible.

Wien’s Law and the Temperature of the Sun

A simple approach is used in an attempt to determine the temperature of the sun by modeling the sun as a blackbody radiator and applying Weins Law. Apparently excellent results are obtained, but the results are false as a consequence of two corrections which cancel out.

Double polarization anisotropy in asymmetric, coupled quantum wells under anisotropic, inplane strain.

A novel coupled-quantum-well system is described in which the inplane, anisotropic strain in successive well layers alternates between compression and tension. A polarization anisotropy in the interband optical matrix elements that arises due to anisotropic strain is reversed between the compressive and tensile cases. Hence, transitions associated with the different well layers have reversed polarization anisotropies. The structure of interest has great flexibility in the energies of successive interband transitions, and in the size of the anisotropy of the various transitions. The structure can be used in describing quantum-well properties, in optical multiplexing, and in devices such as modulators.

Characterization of optical anisotropy in quantum wells under compressive anisotropic in-plane strain

Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is avialable for cases of compressive anisotropic in-plane strain.