Facet degradation of GaN heterostructure laser diodes

Abstract

We investigated the degradation of cleaved facets of (Al,In)GaN laser diodes in different atmospheres. We found that operation in water-free atmospheres with sufficient oxygen shows a slow degradation. Operation in atmospheres with water vapor causes a fast degradation and an oxidation on the facet. This deposition is a permanent damage to the laser diode. If the laser diode is operated in pure nitrogen, we find a thick deposition on the facet, which shows high absorption. This deposition can be removed by either high optical output powers or by operation in atmospheres with sufficient oxygen. We also explain the influence of these coatings to the degradation behavior and see these coatings as the reason for unstable kinks in the L–I characteristics during operation.

Wave guide optimization for homoepitaxial laser diodes

“…The degradation during operation is mainly due to an increase of the threshold current, whereas the differential quantum efficiency stays the same. Only at the end of the lifetime the quantum efficiency is dropping due to a degradation of the contact and the facets, as it has been observed by other groups before [4]. The findings presented above show an increase of device performance due to the better wave guiding in the deep ridge structure.…”

Homoepitaxial laser diodes emitting at 390 nm and the influence of substrate quality

“…Therefore, the degradation mechanism seems to be intrinsic. However, the life time seems to be strongly dependent on the initial current, which is pointing to a current enhanced degradation as it has been observed by other before [5,6]. The usual finding is that the lifetime increases by a factor of more than ten, if one decreases the operation current to half the value [7].…”

Thermally-activated degradation of InGaN-based laser diodes: Effect on threshold current and forward voltage

“…(b) For longer stress times (t > 2000 min), I th increases linearly with stress time. Considered that no current flows through the device during the stress, and that temperature is too low to induce a direct lattice damage, the increase in nonradiative recombination can be ascribed to the absorption of atoms from the surrounding atmosphere, in particular oxygen and hydrogen [9] (devices are stressed in air), or to a thermally-activated degradation of the facets due to external contaminants [10]. These processes differ from the ones described in the previous case, and then their saturation is described by a different time constant.…”