Gerald D. Robinson

Fabrication of refractive microlenses in semiconductors by mask shape transfer in reactive ion etching

Abstract Refractive microlenses are formed in semiconductor materials by transfer of a lens-like shape of reflowed erodable polyimide mask into the substrate by reactive ion etching. Simultaneous monitoring of the etch rates of the mask material and the semiconductor results in precise control of the lens radius of curvature. We demonstrate wafer-scale integration of GaAs microlenses with vertical-cavity laser diodes and InP microlenses with InGaAs photodetectors. These integrated components can be used directly in optical systems without additional external optics.

Calibrated intensity noise measurements in microcavity laser diodes

Calibrated intensity noise measurements of microcavity lasers diodes are presented. Partition noise due to polarization degeneracy is found to render excess noise that destroys squeezing. The measurements indicate that it may be necessary to introduce polarization control to realize sub‐shot‐noise levels in microcavity laser diodes.

Monolithic integration of refractive lenses with vertical-cavity lasers and detectors for optical interconnections

We present a technique for monolithic integration of vertical cavity lasers and detectors with refractive microlenses etched on the back side of the semiconductor substrate in a wafer-scale process. This integration provides collimated or focused laser beam sources for applications in free-space interconnections or for coupling to optical fibers, and it improves the collection efficiency of detectors.

Analysis of VCSEL degradation modes

VCSELs have recently made a great deal of progress both in improved performance with threshold currents now < 100 (mu) A, as well as in their commercialization. Parallel communication links based on VCSEL arrays are now commercially available. However, little information has been published to date on VCSEL reliability or on what causes VCSEL failures. In this presentation, we will describe the VCSEL degradation processes observed in the wide variety of structures we have tested. These include GaAs- and InGaAs-QW VCSELs; top- and bottom-emitting structures; and proton-implanted and etched-pillar VCSELs. We will discuss the novel observation that in most VCSELs we have examined, defects in the upper mirror (a p-type Distributed Bragg Reflector) can be associated with VCSEL degradation. Laser spectra show a luminescence peak from these mirrors, indicating the presence of minority carriers in the low-bandgap layers of the mirrors. These minority carriers are thought to be at the origin of the defect formation in the p-mirrors. We will discuss the possible sources of this minority carrier injection, and present spectra which shed light on the cause of this phenomenon. We will also discuss how fabrication and packaging stresses for some structures significantly accelerate the degradation process. The failure modes observed for various designs will be shown, and possible design improvements suggested.

Small electrically pumped index-guided vertical-cavity lasers

High-yield, reliable electrically pumped index-guided vertical cavity lasers with diameters less than 4 microns have been fabricated using low resistance, alloyed, ring contact metallization. Existing metallization schemes used for bottom emitting vertical cavity lasers (VCLs) tend to be highly resistive, since the top metallization layer serves the dual purpose of mirror and electrical contact. This results in acceptable performance for large diameter devices, but poor performance for smaller devices that operate at higher current densities. Low resistance alloyed ring contacts have been developed for small bottom emitting VCLs that maintain the required optical properties while dramatically improving the electrical properties.<<ETX>>