Electrical and Computer Engineering ETDs

Publication Date

Fall 11-15-2016

Abstract

Semiconductor membranes offer an interesting materials and device development platform due to their ability to integrate dissimilar materials through a print, stamp and transfer process. There is a lot of interest in integrating antimonide based type-II superlattices (T2SL) onto inexpensive substrates, such as Si, to not only undertake fundamental studies into the optical, electronic and structural properties of the superlattices but also to fabricate wafer-level infrared (IR) photodetectors. An effective approach to transfer type-II superlattice membranes (T2SL-M) onto alternate substrates is based on membrane release from the native GaSb substrate followed by the transfer to a new host substrate. In this work, I have transferred InAs/GaSb and InAs/InAsSb T2SLs with different in-plane geometries from a GaSb substrate to a variety of host substrates, including Si, polydimethylsiloxane and metal coated surfaces. Electron microscopy shows structural integrity of transferred membranes with thicknesses ranging from 100 nm to 2.5 µm and lateral sizes from 24x24 µm2 v to 1x1 cm2 . Atomic force and electron microscopy reveal the excellent quality of the membrane interface with the new host. The crystalline structure of the membrane is not altered by the fabrication process, and minimal elastic relaxation occurs during the release step, as demonstrated by X-ray diffraction and mechanical modeling. I have also used the antimonide superlattice membranes to realize wafer level infrared detectors on silicon substrates without using conventional Indium-bump hybridization. In this approach, PIN superlattices are grown on top of a 60 nm Al0.6Ga0.4Sb sacrificial layer on a GaSb host substrate. Following the growth, I have transferred the individual pixels using an epitaxial lift-off technique, which consists of a wet-etch to undercut the pixels followed by a dry-stamp process to transfer the pixels to a silicon substrate prepared with a gold layer. I have done structural and optical characterization of the transferred pixels using an optical microscope, scanning electron microscopy, and photo luminescence. The interface between the transferred pixels and the new substrate is abrupt, and no significant degradation in the optical quality is observed. Next, I have fabricated an indium-bump-free membrane detector using this approach. Spectral response measurements and the current-voltage characteristics of an infrared photodetector, based on the InAs/InAsSb superlattice, bonded to Si demonstrates the functionality of transferred membranes in the infrared range. The performance of the membrane detector is compared to a control detector using the as-grown epitaxial material. The proposed approach to fabricate Indium-bump free detectors could pave the way for wafer-level integration of photonic detectors on silicon substrates, which could dramatically reduce the cost of these detectors. Since the release of T2SL-M is achieved using a high etch selectivity between the active region and the Al-containing sacrificial layers, a poor selectivity between the sacrificial layers and a variety of T2SL active regions will result in significant damage to the active layer of an IR detector. I have developed a novel two-step etching process to protect the T2SL-M while the sacrificial layer is etched away. In this process, both the top surface and the sidewalls of the membrane are coated with a hard-baked polymer film (i.e., photoresist), and therefore they are unexposed to the chemical etchant. For Al and Ga containing compounds, with no membrane isolation, this process leads to rough sidewalls which are expected to increase surface recombination in the membrane and therefore increases the dark current density of an IR detector. I have quantified this effect by characterizing T2SL IR detectors fabricated on isolated and non-isolated mesas. A comparative analysis of the dark current density measured for the two devices signify the effect of having exposed sidewalls during membrane release. These experimental results are consistent with theoretical calculations which show a relative enhancement of surface recombination with increasing roughness of the membrane sidewalls. The development of these Sb based T2SL membranes opens up new exciting prospects for material science studies and device architecture integration.

Keywords

antimonide, membranes, transfer, infrared, integration, two-step etch

Sponsors

University of New MExico

Document Type

Dissertation

Language

English

Degree Name

Electrical Engineering

Level of Degree

Doctoral

Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Prof. Sanjay Krishna

Second Committee Member

Prof. Francesca Cavallo

Third Committee Member

Prof. Ganesh Balakrishnan

Fourth Committee Member

Prof. Ali Javey

Fifth Committee Member

Dr. Edward Smith

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