S. M. Vernon

Hydrogenation of GaAs on Si: Effects on diode reverse leakage current

Plasma hydrogenation for 3 h at 250 °C of GaAs layers grown directly on Si substrates by metalorganic chemical vapor deposition, followed by a 5‐min, 400 °C anneal to restore the passivated shallow donor electrical activity, increases the reverse breakdown voltage of Schottky diode structures from 2.5 to 6.5 V. This improvement appears to be a result of the passivation by atomic hydrogen of defects such as threading dislocations caused by the large (4%) lattice mismatch between GaAs and Si. A reduced Schottky barrier height is exhibited by hydrogenated samples, consistent with As depletion of the surface occurring during the long duration plasma processing.

Thickness dependence of material quality in GaAs-on-Si grown by metalorganic chemical vapor deposition

The evolution with increasing layer thickness of the structural and electrical properties of GaAs grown directly on Si or Si‐on‐insulator (SOI) by metalorganic chemical vapor deposition is reported. There is a substantial improvement in the surface morphology and near‐surface crystallinity of the GaAs in thicker films (≥1.5 μm). The implant activation efficiency of 60‐keV 29Si ions at a thickness of 4 μm is comparable to that seen in bulk GaAs. The deep level concentration is also observed to decrease with increasing layer thickness. Transmission electron microscopy reveals average defect densities near 108 cm−2 in films deposited either on misoriented or exact (100) Si, and in those grown on SOI.

Characterization of InP/GaAs/Si structures grown by atmospheric pressure metalorganic chemical vapor deposition

The thickness dependence of material quality of InP‐GaAs‐Si structures grown by atmospheric pressure metalorganic chemical vapor deposition was investigated. The InP thickness was varied from 1–4 μm, and that of the GaAs from 0.1–4 μm. For a given thickness of InP, its ion channeling yield and x‐ray peak width were essentially independent of the GaAs layer thickness. The InP x‐ray peak widths were typically 400–440 arcsec for 4‐μm‐thick layers grown on GaAs. The GaAs x‐ray widths in turn varied from 320–1000 arcsec for layer thicknesses from 0.1–4 μm. Cross‐sectional transmission electron microscopy showed high defect densities at both the InP‐GaAs and GaAs‐Si interfaces. In 4‐μm‐thick InP layers the average threading dislocation density was in the range (3–8)×108 cm−2 with a stacking fault density within the range (0.4–2)×108 cm2. The He+ ion channeling yield near the InP surface was similar to that of bulk InP (χmin∼4%), but rose rapidly toward the InP‐GaAs heterointerface where it was typically around ...

Heterointerface stability in GaAs‐on‐Si grown by metalorganic chemical vapor deposition

The stability of the electrical and structural properties of GaAs directly deposited on Si by metalorganic chemical vapor deposition is examined. Extended annealing at 900 °C leads to substantial diffusion of Si across the heterointerface while under the same conditions there is no significant motion of Si incorporated as a dopant into the GaAs surface region. The degree of enhancement of Si diffusion ranges from a factor of ∼250 for 0.5‐μm‐thick GaAs films to ∼5 for 4‐μm‐thick films. The annealing time and GaAs layer thickness dependence of Si diffusivity near the interface is consistent with a defect‐modulated mechanism. A large fraction of this mobile Si is electrically inactive.

Selective area epitaxy of GaAs on Si using atomic layer epitaxy by LP-MOVPE

Abstract This paper reports on the effectiveness of selective area epitaxy by conventional MOCVD and atomic layer epitaxy nucleation techniques in improving the quality of GaAs on Si. The GaAs films were deposited through photolithographically patterned openings in the oxide coated Si wafers. Selective epitaxy was found to eliminate wafer warpage, reduce film cracking and reduce the tensile stresses for islands less than 200 μm/side. Complete stress relief has been achieved in 10 μm/side islands after oxide removal. Thermal cycle growth deposition technique has been employed resulting in two orders of magnitude reduction in the dislocation density and excellent surface morphologies. The potential of selective epitaxy, by the above techniques, in improving the quality of the GaAs on Si films is addressed.

Activation characteristics and defect structure in Si-implanted GaAs-on-Si

Undoped metalorganic chemical vapor deposited GaAs layers on Si substrates were implanted with 29Si ions (5×1012 cm−2 dose at 100 keV energy) to form a shallow n‐type region. The net donor activation (74%) and electron mobility (3014 cm2 V−1 s−1) after rapid thermal annealing (900 °C, 10 s) were compared to those obtained for similar implants into bulk GaAs. There was a slight improvement in the proton backscattering yield from the GaAs‐Si interface region after the annealing cycle, consistent with cross‐sectional transmission electron microscopy data showing an alignment of defects in annealed samples.

Characterization of GaAs grown by metalorganic chemical vapor deposition on Si‐on‐insulator

Epitaxial GaAs layers were grown by metalorganic chemical vapor deposition on Si‐on‐insulator structures formed by high dose oxygen implantation. The quality of the GaAs films was examined as a function of layer thickness (0.01–4 μm). The surface morphology, ion backscattering yield, x‐ray diffraction peak width, and Si implant activation efficiency all improve substantially with GaAs thickness. At a film thickness of 4 μm many of these properties are comparable to bulk GaAs, but some cracking of the epitaxial film is evident. Cross‐sectional transmission electron microscopy reveals an average defect density of ∼108 cm−2 in the GaAs layer, which is similar to the density in GaAs films grown directly on Si.

Material and device properties of 3′ diameter GaAs-on-Si with buried P-type layers

Two problems facing GaAs-on-Si grown by metal organic chemical vapour deposition (MOCVD) are firstly, scale up to 3′ and greater wafer diameter with accetaably uniform layer thicknesses and electrical and optical properties, and secondly, the achievement of adequate device isolation through the use of the buffer layers of low doping density (less than or equal to 1014 cm−3). We have investigated the thickness uniformity and 300 K photoluminescence intensity of 3′ diameter, MOCVD-grown GaAs layers on silicon substrates by whole wafer mapping of these parameters, and correlate the variations found with the gas flow direction during deposition of the GaAs. We have overcome the high background doping densities (n = 5–20) × 1015 cm3) in the material by a buried beryllium implant (1–5)×1012 at 120 keV) followed by 850°C, 3 s annealing. This provides adequate isolation for MESFETs, and we fabricated such devices with gms of 160–175 mS mm−1 using our standard process. These values are similar to homoepitaxial MESFETs fabricated in the same way.

Material and Device Properties of 3” Diameter GaAs-on-Si with Buried P-type Layers

Two problems facing MOCVD grown GaAs-on-Si are firstly, scale up to 3” and greater wafer diameter with acceptably uniform layer thicknesses and electrical and optical properties, and secondly the achievement of adequate device isolation through the use of buffer layers of low doping density (≤10 14 cm −3 ). We have investigated the thickness uniformity and 300K photoluminescence intensity of 3” O, MOCVD grown GaAs layers on Si substrates by whole wafer mapping of these parameters, and correlate the variations found with the gas flow direction during deposition of the GaAs. We have overcome the high background doping densities (n =5−20 × 10 15 cm 2 ) in the material by a buried Be implant (1−5 × 10 12 at 120 keV) followed by 850°C, 3 sec annealing. This provides adequate isolation for MESFETS and we fabricated such devices with g m s of 160-175 mS mm −1 using our standard process. These values are similar to homoepitaxial MESFETS fabricated in the same way.

Photoluminescence of InP/GaAs/Si Heterostructures

Low temperature photoluminescence results from MOCVD epitaxial InP grown on GaAs/Si substrates are presented as a function of thickness of the GaAs buffer layer. As a consequence of thermal expansion mismatch of the heterostructure, the InP layer contains residual stress which causes the band gap to shift and splits the valence band degeneracy of the m j = ± 3/2 and the m j = ± 1/2 bands. Both the shifting and splitting phenomena are clearly seen in tite PL results and are shown to depend on the GaAs buffer layer thickness.