Micro-opto-electromechanical systems (MOEMS) based on micromechanical mirrors can be used as key elements for
light guiding, steering and concentration. We propose micromechanical mirror arrays for light concentration on
photovoltaic modules. The semiconductor materials for solar cells are the most expensive components of a photovoltaic
system. One of the ways to reduce cost is to use light concentration by focusing sunlight onto small solar cell areas using
optical components such as lens systems. The whole system requires an external rotation mechanism to track the suns
position. As an alternative, we propose and implemented micromachined mirror arrays to concentrate light. This allows
precise dynamic light steering onto the solar cell module. These micromirror arrays can be electrostatically tuned to track
the sun position or the maximum of the brightness distribution in the sky. The micromirror arrays are located in a sealed
environment and, therefore, insensitive to external influences, such as atmosphere and wind. The advantages of the
micromachined mirrors based concentrator photovoltaic systems are dynamic light steering onto solar cells, mass
production compatibility, long lifetime and low cost. The concept of the micromachined mirror arrays will be presented.
InP based tunable optical MEMS devices, such as Fabry-Perot filters, VCSELs, photodiodes, consist of two distributed
Bragg reflectors (DBRs) and a cavity. Tuning of the filter wavelength is achieved by electrostatic actuation of the two
DBRs which are p-doped and n-doped, respectively, and reversely biased. The cavity and the DBRs consist of a stress
compensated InP/airgap structure which is fabricated by sacrificial layer removal, using FeCl3 wet etching of InGaAs
layers. In this work we investigated the influence of p-and n-type conductivity on the etching process. We observed that
the sacrificial layer etch rate of n-InGaAs is 7 times slower than the p-InGaAs. This influences the stress in the n-DBR
section of the tunable device. Based on these results novel wavelength tunable optical devices with multiple InP
membrane/airgap structures will be designed.
We present the results on the monolithic integration of self-assembled GaAs micromirrors with light emitting diodes. The micromirrors were self-assembled by the strain-driven mechanism, which control the micromirror standing position and flatness. The device epi-layer structure and the fabrication processes were optimized. Self-locking mechanism was also employed to precisely position and enhance the mechanical strength of the assembled micromirrors. Light emission was observed on the integrated devices. For the first time, the effectiveness of the self-assembled micromirrors was confirmed in the monolithic integration with LEDs on GaAs. This result shows the feasibility of GaAs-based micro-opto-electromechanical systems for photonics applications.
We report the high-density light-emitting diodes (LEDs) using lateral junction for LED printer and other applications. Semi-insulating GaAs (311)A substrates were patterned to create (100) sidewall. GaAs/AlxGa1-xAs epilayers were grown on the patterned substrate using the amphoteric silicon as a dopant, which forms the lateral p-n junction. For the first time, high-density (2400 dots per inch) LED arrays were fabricated using the lateral junction with device width of 10.6 micron. Light emission spectrum shows a single peak at a wavelength of 813 nm with FWHM of 56 nm at room temperature. The same method can be used to fabricate LED arrays with higher device densities for applications in high resolution LED printers, displays and other applications.