Physics Chat
Determining the impact of facet roughness on etched facet InP laser devices
Speaker: Tristan Burman (Prof Peter M Smowton's group)
Date: Thursday 23 February 2023
Time: 14:30
Venue: Translational Research Hub Seminar Room 0.01
Optoelectronics are currently going through a period of development similar to that seen in electronics over the last fifty years, devices are being miniaturised and integrated circuits are being developed with an increasing number of functions on chip. Laser devices are considered to be one of the more difficult components to integrate, and further research is required to produce an efficient manufacturing process that can be applied to large substrates for dense integration of lasers. Typically, the laser facets are manufactured via cleaving, this process breaks the wafer into pieces and is therefore inappropriate for monolithic integrated circuits.
Using etching to manufacture the laser facets overcomes the integration issue however each come with their own draw backs. Wet etching is unable to reliably produce the vertical profile required for laser facets. Dry etching can achieve the vertical profile using methods preferred by large scale manufacturing however, it does tend to introduce a sidewall roughness that the manufacture process must be optimised to reduce. The impact that the sidewall roughness has on facet reflectivity and therefore device performance is yet to be fully understood. There are commonly held beliefs that an RMS roughness below the emission wavelength divided by an arbitrary value will produce a tolerable loss in efficiency [1]. There are also models that that attempt to better relate an RMS roughness of a surface to its reflectivity [2]. These models are often used to determine a facets reflectivity from a roughness measurement or vice versa. However, they are developed for a single material system and rarely verified on real world devices.
This work independently determines the facet reflectivity and roughness of InP lasers operating at telecom wavelengths manufactured on 100mm wafers, and comparing results to the theoretical models.
References:
1. Francis, D. A., et al. Effect of facet roughness on etched facet semiconductor laser diodes. Applied Physics Letters 68, 1598-1600 (1996).
2. D. A. Stocker, et al. Facet roughness analysis for InGaN/GaN lasers with cleaved facets, Applied Physics Letters 73, 25-1927 (1998).