F.E. Ejeckam

Lattice engineered compliant substrate for defect-free heteroepitaxial growth

Presented here is proof-of-principle that a thin single crystal semiconductor film—when twist-wafer bonded to a bulk single crystal substrate (of the same material)—will comply to the lattice constant of a different single crystal semiconductor thick film grown on its surface. In our experiment, a 100 A film of GaAs was wafer bonded to a GaAs bulk substrate, with a large twist angle between their 〈110〉 directions. The resultant twist boundary ensures high flexibility in the thin film. Dislocation-free films of In0.35Ga0.65P(∼1% strain) were grown with thicknesses of 3000 A, thirty times the Matthews–Blakeslee critical thickness, on twist-wafer-bonded films of GaAs.

Dislocation-free InSb grown on GaAs compliant universal substrates

An innovative compliant GaAs substrate was formed by wafer bonding a 30 A GaAs layer to a bulk GaAs crystal with a large angular misalignment inserted about their common normals. InSb epitaxial layers, which is about 15% lattice mismatched to GaAs, have been grown on both compliant substrates and conventional GaAs substrates. Transmission electron microscopy studies showed that the InSb films grown on the compliant substrates have no measurable threading dislocations, whereas the InSb films on the conventional GaAs substrates exhibited dislocation densities as high as 1011u2009cm−2. The observations made here suggest that the defect-free heteroepitaxial growth of exceedingly large lattice-mismatched crystals can be achieved with compliant universal substrates.

High‐performance InGaAs photodetectors on Si and GaAs substrates

In this work, we demonstrate record low dark current operation of InGaAs (1.55 μm) p‐i‐n photodetectors on both silicon and gallium arsenide substrates using a wafer bonding technique. The photodetectors were made by first bonding the p‐i‐n epitaxial layers to the Si and GaAs substrate followed by chemical removal of the host (InP) substrate from the p‐i‐n structure. The photodetector was then fabricated atop the newly exposed p‐i‐n epilayers. Dark currents of as low as 57 pA on a GaAs substrate and 0.29 nA on a Si substrate were measured under 5 V reverse bias. The responsivity at 1.55 μm wavelength was measured to be 1 A/W, corresponding to an external quantum efficiency of 80%. The series resistance measured across the bonded interface gave 17 Ω on GaAs and 350 Ω on Si, respectively.

Growth of InGaAs multi-quantum wells at 1.3 μm wavelength on GaAs compliant substrates

InGaAs multiple quantum wells at 1.3 μm wavelength have been grown on a twist-bonded GaAs compliant substrate. The GaAs compliant substrate contains a 30 A GaAs thin layer bonded to a GaAs bulk substrate with a 22-degree angle. Nomarski phase contrast microscopy, transmission electron microscopy (TEM), and photoluminescence were used to characterize the heteroepitaxial layers. The smooth and crosshatch-free surface morphology, dislocation-free cross-sectional TEM, and strong luminescence intensity all provide convincing evidences for substantial improvement of the quality of heteroepitaxial material using the compliant substrate technique. Research is underway to apply the concept and technique of compliant substrate to Si and other materials.

Wafer bonding technology and its optoelectronic applications

This paper describes the wafer bonding technology and its applications to optoelectronic devices and circuits. It shows that the wafer bonding technology can create new device structures with unique characteristics and can form integrated optoelectronic circuits containing optical, electronic and micro-mechanical devices.

Wafer bonding and its application on compliant universal (CU) substrates

We have recently found a novel and significant application for the wafer bonding technology. We demonstrated that by bonding an ultra thin layer of semiconductor to a bulk crystal with a rotational angle along their surface normal, this new structure can achieve interesting behaviors as a compliant substrate. When heteroepitaxial layers are grown on such twist-bonded substrates, the bonded thin layer is plastically deformed to relax the strain before threading dislocations are nucleated in the heteroepitaxial layer. This is a new and energetically more favorable way for lattice strain relaxation and is unique to the twist-bonded structure. We found that this concept can be applied to many semiconductors such as GaAs and Si to form compliant substrates where heteroepitaxy of exceedingly large lattice mismatch (e.g. 15%) can be grown without defects. This implies that twist-bonded compliant substrates may, to a large extent, function as a universal substrate for growth of high quality materials of nearly any lattice constant.

Misaligned (or twist) wafer-bonding: a new technology for making III-V compliant substrates

We show from theoretical calculations and modeling that intentionally misaligned (or twist) wafer-bonding can be used to increase the critical thickness of a III-V thin film by several orders of magnitude. In conventional III-V wafer-bonding for optoelectronics, the facets of two single crystal wafers are aligned with each other before bonding in order to facilitate wafer-cleaving and further device-processing. To the authors knowledge, the peculiar case of intentional misalignment between two bonded wafers facets has not been reported for III-V single crystal wafers. We propose and model a new type of substrate (hereafter known as a compliant substrate) platform to be used for lattice-mismatched dislocation-free heteroepitaxial growth. In forming the compliant substrate, a thin-film (/spl sim/100 /spl Aring/) of a certain III-V compound is bonded to a bulk substrate of the same material, with a small angle placed between their ~011 facets. The misalignment allows the film to relax via a network of screw dislocations in the twist-boundary.

Wafer bonding technology and its applications in optoelectronic devices

The new optoelectronic integrated technology--wafer bonding is described. The results of wafer bonding and applications in several new types of optoelectronic devices are presented.

High-performance InGaAs photodetectors on Si and GaAs substrates

In this work, we demonstrate record performance operation of long wavelength (1.55 /spl mu/m) P-I-N (InP-InGaAs-InP) photodetectors on both Silicon and Gallium Arsenide substrates using a wafer bonding technique. The photodetectors were made by first bonding the P-I-N epitaxial layers to the Si and GaAs substrates followed by chemical removal of the host (InP) substrate from the P-I-N structure. The photodetectors were then fabricated atop the newly exposed P-I-N (InP-InGaAs-InP) epilayers. Dark currents of as low as 57 pA on a GaAs substrate and 0.29 nA on a Si substrate were measured under 5 V reverse bias. The responsivity at 1.55 /spl mu/m wavelength was measured to be 1 A/W, corresponding to an external quantum efficiency of 80%. The series resistance measured across the bonded interface and P-I-N layers gave 17 /spl Omega/ on GaAs and 350 /spl Omega/ on Si, respectively.

Compliant universal (CU) semiconductor substrates for III-V and Si Optoelectronics

where E is the thermo-mechanical axial strain in the optical fiber core, P,, are the strain-optic constants v is the Poissons ratio for the fiber, n is the effective refractive index of the fiber that the propagating mode sees, and 5 is the thermo-optic coefficient of the fiber. Because most of these constants remain fairly constant for the different fibers except for the thermooptic effect (e), the above equation can be simplified to