III-V, Si & Ge Epitaxy Lab

The III-V, Si, and Ge Epitaxy Laboratory, together with the III-V and Si Cleanroom Technology, forms a central component of the Center for High Efficiency Solar Cells at Fraunhofer ISE.

In our laboratory, we offer services for the epitaxy of III-V and IV semiconductors on various wafer formats (from 4″ round to M6 square) and substrates such as Si, Ge, InP, and GaAs. Our services include process support, consulting, training, and expert reports. Also a part of our service portfolio is the comprehensive structural and electrical characterization of layer systems and free-standing epitaxial layers. In addition, we offer the preparation of wafers for homo- or heteroepitaxial growth using wet chemical (e.g., special cleaning or electrochemical porosification) and thermal pretreatments.

To this end, we utilize flexible, industry-standard equipment in a high-purity process environment – ensuring the highest quality while maintaining great flexibility.

Our customers include both equipment and component manufacturers as well as manufacturers of epitaxially grown semiconductor structures. Through our close collaboration with the Laboratory for Cleanroom Technology and PV-TEC, we focus our work particularly on the areas of solar cells and laser power cells, aligning our efforts with the specific needs of our manufacturing industry clients.

Our Services in the "III-V, Si & Ge Epitaxy Lab« Include:

• Epitaxy of III-V Semiconductors on Ge, InP, and GaAs Substrates
• Epitaxy of Si, Ge, and SiGe
• Electrochemical Etching and Reorganization of Semiconductors
• Material Characterization of III-V Semiconductor Compounds
• Surface Preparation and Removal

Two multi-wafer reactors from Aixtron (Planetary Reactor G4 & Close Coupled Showerhead Crius) are available for the epitaxy of arsenides and phosphides. Epitaxy is performed on Ge, GaAs, InP, or Si substrates, and for mixed crystals composed of Al, Ga, In, As, P, and Sb, we achieve very high material quality for undoped layers as well as for those with n- or p-doping. We possess particular expertise in the areas of heteroepitaxy directly on germanium or silicon, as well as the metamorphic growth of materials with a bandgap between 2.1 eV and 0.74 eV.

We use an LPE/ASM reactor (LPE2061S) for the epitaxy of Si and Ge layers. This dual-chamber reactor allows us to coat wafers in 4“, 6”, and M6 sizes. We use chlorosilanes (HSiCl₃, SiCl₄, and GeCl₄) as precursors and diborane (B₂H₆) and phosphine (PH₃) for doping. Epitactic Si and Ge layers are characterized, among other things, by the fact that we can adjust the doping profile across the thickness of the wafer by controlling the doping gas flow during growth.

A wet chemistry line in a cleanroom is available for wafer preparation. For characterization purposes, structural etching can be performed and cross-sections can be prepared. In addition, several optical microscopes with AI-controlled analysis masks, electron microscopes (including ion beam polishing), atomic force microscopes, Raman spectrometers, and X-ray diffraction instruments are available for structural investigations. For the electrical characterization of thicker layers, we can produce freestanding samples.

Electrochemical etching of single- and multi-layer porous films is performed using hydrofluoric and acetic acids. At the AMMT facility, we primarily etch germanium using bipolar processes (4-inch wafers). The LayTEC system is equipped with single-sided illumination for light-assisted etching (wafer sizes 4“, 6”, 12", and M6). We use this system for edge-free etching of silicon and silicon carbide. For pre- and post-cleaning, we have a wet chemical line in a cleanroom and a rinser-dryer at our disposal.

Thermal post-processing is performed either in an epitaxial reactor under pure hydrogen or in thermal systems under an N₂ or Ar atmosphere. For structural characterization, we primarily use electron microscopy and X-ray diffraction. The porous layer stacks can also be reconstructed in 3D using the dragonfly© software from individual images created by ion beam polishing.

A wide range of analytical methods and measuring instruments are available for epitaxial development and quality control, starting with in-situ metrology during the MOVPE process. Ex-situ, doping concentrations can be determined using ECV or Hall measurements. Structural characterization is performed using AFM and HR-XRD. Additionally, photoluminescence-based characterization methods are established (wafer mapping (intensity and peak wavelength), power spectra, and transients). Defect characterization can be performed using spectroscopy (DLTS), ECCI (electron channeling contrast imaging), and cathodoluminescence. Material development is supported by electro-optical simulation capabilities to accelerate the development of devices.

Before we detach epitaxially grown layers of silicon or germanium, we define the surface using a diamond blade saw or a laser. In addition, we can measure the highly porous separation layer in advance using an ultrasonic setup and visually depict its homogeneous formation.

For the mechanical removal of the layers, we have a manual setup and a semi-automatic setup (both for wafer sizes up to M6) at our disposal. After successful removal, we can automatically measure and categorize the attachment points using an optical microscope.