No abstract

High speed fiber optic transceiver modules using parallel optics require that oxide-confined vertical-cavity surfaceemitting lasers (VCSELs) be moisture resistant in non-hermetic environments. Conventional storage 85/85 (85°C and 85% relative humidity) testing without a bias does not adequately characterize oxide VCSEL's moisture resistance. Oxide VCSELs do not fail or degrade significantly under such conditions. With a bias, however, we have found that moisture can cause failure modes not seen in dry reliability testing. Without proper device design and fabrication, these failure modes lead to high failure rates in oxide VCSELs. In this paper, we first discuss the failure mechanisms we have identified, including dense dislocation network growth, semiconductor cracking and aperture surface degradation, all in high humidity and high temperature under operating conditions. We then report the results of environmental reliability tests on Agilent's oxide VCSELs developed for the parallel optics modules. The results from a large number of wafers produced over an extended period of time have shown consistent, robust environmental reliability.

Measurements of the current-voltage characteristics of GaAs-AlxGa1−xAs heterojunction layers are reported. The experimental results are consistent with the idea of real-space transfer of the electrons out of the GaAs into the AlxGa1−xAs under hot-electron conditions. Current saturation and negative differential resistance are observed as predicted by Monte Carlo simulations.

Oxide VCSELs are the emitter of choice for high-speed optical communication applications. A low divergence circular beam, wafer-level testing and the capability to create dense two-dimensional arrays provide the VCSEL with unique advantages over edge emitting lasers, such that VSCELs have become a significant part of the optical communication market. An equally important metric for VCSELs is field reliability since significant failure rates are unacceptable for implementation of reliable networks.In order to better understand potential failure paths of VCSELs during field use, a variety of failures have been intentionally created on oxide VCSELs made from AlGaAs / GaAs materials operating at 850nm. Failures were created with epitaxial defects, scratches, surface contamination, thermal shock , ESD and elevated temperature and humidity (85C/85% humidity). We will present the results of these intentional failures, assess high-probability failure paths and compare and contrast the various failure mechanisms.

Electrostatic Discharge (ESD) damage is considered to be the leading cause for IC field failures. With increasing integration densities, devices tend to become more and more sensitive to ESD events. This observation holds particularly true for 850nm VCSELs, as the quest for higher modulation frequencies calls for shrinking device dimensions, aperture sizes in particular.This publication is geared towards an understanding of the various factors that lead to ESD-related failures of oxide VCSELs. A broad variety of current VCSEL product lines at Agilent have been investigated in respect to their ESD resistance and related long-term reliability. Intentionally stressed devices have been characterized in terms of their electrical, optical and visual failure patterns as well as the medium time-to-failure. Cross-sectional and plan-view TEM have been employed to localize ESD damage and its propagation. For the first time, emission microscopy has been used to study the electroluminescence pattern of damaged VCSELs at very low currents. The paper will conclude by listing experimental signatures allowing for differentiation between ESD and other failure modes. Based upon these, effective screening methods are proposed.