Browse Prior Art Database

Method of Making a Silicon Based Photodetector by Incorporating Germanium Dots

IP.com Disclosure Number: IPCOM000012804D
Original Publication Date: 2003-May-28
Included in the Prior Art Database: 2003-May-28
Document File: 5 page(s) / 68K

Publishing Venue

Motorola

Related People

Shawn G. Thomas: AUTHOR [+2]

Abstract

We describe a method for realizing a photodetector, having absorption in the 1.3 – 1.55mm wavelength regime, which is compatible with standard Si manufacturing processes and incorporates dislocation-free Germanium dots as the absorption volume. In the preferred embodiment, the detector is a normal incidence device, but not limited to this configuration. Implementation of the detector utilizes selective epitaxial growth for pre-determined placement of the Germanium dots followed by standard Si processing steps to realize the functional device.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 33% of the total text.

Method of Making a Silicon Based Photodetector by Incorporating Germanium Dots

Shawn G. Thomas and Thomas E. Zirkle

Abstract

                    We describe a method for realizing a photodetector, having absorption in the 1.3 – 1.55mm wavelength regime, which is compatible with standard Si manufacturing processes and incorporates dislocation-free Germanium dots as the absorption volume.  In the preferred embodiment, the detector is a normal incidence device, but not limited to this configuration.  Implementation of the detector utilizes selective epitaxial growth for pre-determined placement of the Germanium dots followed by standard Si processing steps to realize the functional device.

Introduction

For long haul, high bit rate optical communications applications, InGaAs or InGasAsP on InP substrates has been the preferred choice of materials for realizing detectors due to its absorption in the 1.3 – 1.55mm wavelength regime.  However, with Si based technology being the primary driver of the electronics industry, it is desirable to achieve a Si based solution for optoelectronics at 1.3 – 1.55mm to increase the potential for on-chip integration and to provide a cost reduction compared to the current III-V materials solutions.  Silicon, on its own, is not a candidate at 1.3 – 1.55mm since its bandgap of 1.14eV makes it transparent at these wavelengths.  Germanium, on the other hand, has an indirect bandgap of 0.67eV and an almost direct gap of 0.81eV making it a potential candidate for photodetectors in the 1.3 – 1.55mm wavelengths.  Germanium also has the advantage of being compatible with Si process technology. 

The challenge in integrating a thick absorption layer of pure, epitaxial Ge on a Si substrate is in overcoming the lattice mismatch between the two materials.  Due to the 4% lattice mismatch between Si and Ge, the thickness of pseudomorphic Si1-xGex films grown on Si substrates exponentially decreases with increasing Ge concentration so as to be thermodynamically stable.  As such, the critical thickness for pure Ge on a Si substrate is on the order of 10-15Å whereas a thickness of at least 1mm is required for realizing an efficient photodetector.

Method Description

                    The growth of Germanium on a Silicon substrate can occur in two different growth modes depending upon the substrate conditions: (1) Volmer-Weber and (2) Stranski-Krastanov.  The Stranski-Krastanov growth mode (depicted in Fig 1(a)) is characterized by a two-dimensional layer by layer growth followed by three-dimensional island growth once the film has reached a critical strain level.  The 3D island growth acts as a strain relieving mechanism for the Ge film.  The Volmer-Weber growth mode is a purely 3D islanding growth mode and typically occurs at high substrate growth temperatures.

Figure 1.  Depiction of (a) Stranski-Krastanov growth mode and (b) Volmer-Weber growth mode.

The critical feature of this disclosure is the utilization of the...