Dry etching and surface passivation techniques for type-II InAs/GaSb superlattice infrared detectors

Abstract

Two of the key challenges in the realisation of focal plane arrays based on type-II InAs/GaSb superlattices (T2SL) are the difficulty in achieving a good sidewall profile and the increased dominance of surface leakage current as the device dimensions shrink. We report the electrical and morphological results of test pixels for mid-wave infrared T2SL photodiodes etched using a Cl 2 /Ar based inductively coupled plasma reactive ion etching (ICP-RIE) process and passivated using SU-8 epoxy photoresist. The etch rate and sidewall surface morphology of GaSb, InAs, and InAs/GaSb T2SL materials are compared after dry etching under the same conditions, leading to the determination of an optimal etch rate. The effect of surface treatment using selected wet chemical etchants before passivation on the surface leakage current is presented. Limitations of the dry etching recipe and further improvement of the sidewall verticality and smoothness are also discussed. Good sidewall profiles and bulk-limited dark currents are demonstrated for T2SL photodiodes etched to depths between 1.5 and 3.5 μm with a pitch size down to 12 μm.

Inductively Coupled Plasma Etching of Complementary Barrier Infrared Detector Focal Plane Arrays for Long-Wave Infrared Imaging

“…The importance of etch parameters in achieving clean sidewalls, smooth surface morphology, and anisotropic etching on the device performance of SL detectors has been reported [1]- [3]. However, there have been no discussions on external factors that play an equally important role on the device performance.…”

Pretreatment for surface leakage current reduction in type-II superlattice MWIR photodetectors

“…Especially, mesa formation and passivation with understanding of surface leakage mechanism is critical issue. So far, many researchers have mentioned the mesa formation method [4]- [6] and passivation to mesa sidewall [7]- [11]. Inductive coupling plasma (ICP) etching with chloride gas is usually adopted to form mesa structure.…”

Inductively coupled CH 4 /H 2 plasma etching process for mesa delineation of InAs/GaSb type‐II superlattice pixels

“…The development of next‐generation FPAs requires high packing density of detector pixels with small pitch size that creates a need for a mesa delineation technique capable of producing deep and vertical mesa sidewalls. ‐based reactive ion etching (RIE) is widely used for delineation of the T2SL pixels [3]. However, low volatility of etch products formed during etching leads to rough surfaces and also results in bevelled sidewall profiles of the T2SL pixels which thus creates challenges for etching deeper structures with smaller inter‐pixel width <2 μm [3].…”