Effect of cylindrical geometry on the wet thermal oxidation of AlAs

Abstract

We have investigated the wet thermal oxidation of AlAs in cylindrical geometry, a typical configuration for vertical-cavity surface-emitting lasers. Through both experiment and theoretical calculations, we demonstrate a significantly different time dependence for circular mesas from what has been reported in the literature both in studies of stripes and in a study of circular mesas. We attribute this different time dependence to the effect of geometry on the oxidation.

Controlled formation of oxide shells from GaN nanowires: Poly- to single-crystal

“…The difference in O 2 pressure, which is due to the concentration of the oxidizing agent, is the decisive factor in the improvements when the shells are formed in a diffusion-driven process. [23,24] After the initial oxidation of the surface of the GaN nanowire, the whole process is assumed to undergo the following stages (as schematically illustrated in Fig. 4) [23] : diffusion of O 2 through the already oxidized surface of the Ga 2 O 3 layer; a subsequent oxidation reaction at the Ga 2 O 3 / GaN interface; and the accompanying inward growth of the Ga 2 O 3 layer.…”

Strain in wet thermally oxidized square and circular mesas

“…However, until recently, studies of the oxidation process have been concerned primarily with the simpler case of stripes. As demonstrated in several recent reports, [4][5][6] oxidation proceeds much differently in circular mesas than in stripes. It can also be shown that the oxidation process has a unique timedependence for square mesas.…”

Modelling anisotropic lateral oxidation from circular mesas

“…The procedure to implement the model with an anisotropic reaction (and an isotropic diffusion and convection) is based on the iterative use of Eq. (5) to (7) with { �⃗ } defined in (11) and (12). It relies on understanding that the progression of the oxidation front with time is the result of a succession of an ensemble of elementary point-like oxidations of duration, dt, whose local extent around the point, ⃗, in the direction, ϕ, is given by…”

“…depend on the geometrical characteristics of the interface between the (unoxidized) semiconductor and the oxidized areas resulting from the partial lateral oxidation of mesas whose etched sidewalls have been exposed to water. To address the above-mentioned requirement and potentially enhance the device manufacturability, several models have been developed to reproduce the process kinetics [12] [13] [14] [15] [16] [17] [18] [15] [19] [20] [21] [22]. These models are, in essence, all based on the empirical model established by Deal and Grove which describes and quantifies the temporal evolution of the oxidation depth of surface oxidized silicon wafers in terms of the interplay between the diffusive and reactive nature of the process [23].…”

“…As the Al-III-V semiconductor oxidation progresses laterally from the sidewalls of etched mesas rather than from the wafer surface, the reported models have primarily been concerned with the extension from one dimension to 2-to-3-dimensions as well as with the analysis of the associated consequences. It has thus been shown that the process kinetics depends on the etched mesa geometry [12] [13] [14] [15] [16] [17], on the thickness of the to-be-oxidized layer [18] [15] [19] [20] and of its (oxidizing) surroundings [21] [22]. In all these models, the process is assumed to be isotropic and, therefore, the shape of the oxide aperture would then readily be inferred from the etched mesa geometry by a homothetic transformation.…”