W. Z. Cai

Demonstration of a GaAs-based compliant substrate using wafer bonding and substrate removal techniques

A GaAs-based compliant substrate that uses an intermediate AlGaAs-oxide layer to separate thin 150 /spl Aring/-1000 A GaAs compliant layers from a GaAs host substrate is described. The compliant substrates and epitaxial layers of lattice-mismatched In/sub 0.15/Ga/sub 0.85/As were studied using atomic force microscopy and double-crystal X-ray diffraction. The surface morphology of the 1000 A compliant substrate prior to growth had an RMS and peak-to-peak roughness of 10 /spl Aring/ and 100 /spl Aring/. Following growth of 3000 /spl Aring/ In/sub 0.15/Ga/sub 0.85/ the root mean square (RMS) roughness increased to 50 /spl Aring/, and slip lines were observed in the [110] direction. A comparison of lattice-matched p/sup +/-n junction diodes grown on a substrate with a 1000 /spl Aring/ compliant layer and a standard GaAs substrate revealed similar dark current-voltage characteristics, which demonstrate the high quality of the compliant substrate.

Molar fraction and substrate orientation effects on carbon doping in InGaAs grown by solid source molecular beam epitaxy using carbon tetrabromide

Carbon incorporation in InGaAs and GaAs is systematically studied in solid-source molecular beam epitaxy (MBE) as a function of carbon tetrabromide pressure, indium molar fraction, and substrate orientation. The maximum attainable free carrier concentration in GaAs and InGaAs lattice matched with InP was 2×1020 cm−3. The etching effect of CBr4 on growth rate reduction, surface morphology, and growth mechanism is clarified. A comparative study of carbon incorporation as function of substrate orientation and polarity was undertaken by the growth of GaAs and In0.53Ga0.47As on (n11)A and B (n=2, 3, 5) and (100) oriented substrates. Free carrier concentration and mobility measurements showed no carbon autocompensation in GaAs but strong amphoteric behavior for In0.53Ga0.47As grown on arsenic terminated planes. Measurement of hole concentration as function of indium molar fraction in InxGa1−xAs shows that carbon tetrabromide can be used as an effective acceptor doping percursor for indium molar fraction x less ...

A comparative study of carbon incorporation in heavily doped GaAs and Al0.3Ga0.7As grown by solid-source molecular beam epitaxy using carbon tetrabromide

The electrical properties of carbon doped GaAs and AlGaAs were studied as a function of substrate temperature and CBr4 flux for the doping range ∼1018–1020 cm−3. Hall measurements indicate a strong reduction in the free carrier concentration of GaAs films grown with the same CBr4 flux at substrate temperatures above 620 °C. Secondary ion mass spectroscopy measurements, however, show no reduction of chemical carbon concentration. The electrical properties of GaAs:C epilayers grown on (n11)A and B surfaces, where n=2–5, show strong dependence on crystallographic orientation. Based on these measurements, the model of free carrier concentration reduction in GaAs:C based on formation of electrically inactive C–C pairs has been proposed. In contrast, no anomalous carbon incorporation in AlGaAs has been detected for the doping range ∼1018–1020 cm−3 and the substrate temperature range 550–700 °C. The resulting material exhibits excellent transport and optical properties.

Heavily carbon-doped In0.53Ga0.47As on InP (001) substrate grown by solid source molecular beam epitaxy

Heavily carbon-doped In0.53Ga0.47As with hole densities between 5.6×1018 and 2.1×1020 cm−3 has been grown by solid source molecular beam epitaxy on InP. The dependence of carbon tetrabromide (CBr4)-induced lattice mismatch upon the atomic carbon concentration has been determined from x-ray rocking curve measurements. It has been found by secondary ion mass spectroscopy that the alloy composition is altered by the preferential etching effect of CBr4. After taking into account this compositional change, the “intrinsic” lattice contraction solely due to carbon incorporation has been obtained, which obeys Vegard’s law.

Lattice mismatched molecular beam epitaxy on compliant GaAs/AlxOy/GaAs substrates produced by lateral wet oxidation

Large-area 16 nm GaAs-Al x O y -GaAs substrates were formed by lateral wet oxidation of patterned GaAs/Al 0.97 Ga 0.03 As/GaAs heterostructures. Wet digital etching followed by in situ dry iodine etching was used to prepare thin GaAs layers intended to serve as compliant substrates. Relaxed layers of In 0.15 Ga 0.85 As were deposited on the compliant substrates and on bulk GaAs substrates using In 0.15 Ga 0.85 As and In 0.15 Al 0.85 As nucleation layers. The In 0.15 Ga 0.85 As epitaxial layers grown on the compliant substrates using an In 0.15 Al 0.85 As nucleation layer showed no crosshatch pattern by Nomarski microscopy and had X-ray rocking curve linewidths that were narrower than those grown on bulk GaAs or on samples with In 0.15 Ga 0.85 As nucleation layers.

Electrical properties of molecular beam epitaxially grown AlxGa1−xSbyAs1−y and its application in InP-based high electron mobility transistors

We have investigated the use of lattice-matched AlxGa1−xSbAs quaternary alloys in InP-based microelectronic devices. The band alignment for AlxGa1−xSbAs/InGaAs is calculated across the entire compositional range of x using van de Walle and Martin’s model solid theory, and the theoretical predictions agree with previously published values within 0.1–0.3 eV. Temperature-dependent current–voltage measurements are carried out on Au/Cr/AlxGa1−xSbAs Schottky diodes grown by molecular beam epitaxy. From an Arrhenius analysis, an effective barrier height of 0.67–0.79 eV is obtained, which decreases as the x increases in the range of 0.5⩽x⩽0.9. For the first time, InAlAs/InGaAs high electron mobility transistors are fabricated with an AlxGa1−xSbAs barrier enhancement layer. A reduced gate leakage and delay of gate forward turn-on are attributed to the incorporation of AlxGa1−xSbAs. The effectiveness of AlxGa1−xSbAs is more pronounced for x=0.5 and 0.7 than for x=0.9.

MBE growth of near-infrared InGaAs photodetectors with carbon tetrabromide as a p-type dopant

The carbon doping of In/sub x/Ga/sub 1-x/As was systematically studied as a function of carbon tetrabromide flux and indium molar fraction. The efficiency of carbon incorporation in InGaAs lattice matched with InP was the same as GaAs and showed a maximum attainable doping level of 2/spl times/10/sup 20/Cm/sup -3/. The increase of indium molar fraction showed autocompensation and a switch of conductivity from p-to-n-type, at an In molar fraction of 80%. In/sub 0.73/Ga/sub 0.27/As photodetectors were fabricated using carbon as a dopant. The figures of merit of the p-i-n photodetectors showed parameters close to those of beryllium doped devices. CBr/sub 4/ can be used as an effective p-type doping precursor in solid-source molecular beam epitaxy in In/sub x/Ga/sub 1-x/As with indium molar fraction up to 80%.

Iodine-assisted molecular beam epitaxy

Abstract Iodine was introduced into our solid source molecular beam epitaxy chamber during the growth of GaAs and AlGaAs layers and strained-layer InGaAs quantum wells. Photoluminescence spectra of these samples taken at 4.2 K were compared to spectra from a series of test samples which were grown in the absence of iodine flux. We have observed a general improvement of the material quality of AlGaAs layers grown at substrate temperatures around and below 600°C since the introduction of iodine into our chamber regardless of whether an iodine flux impinged on the substrate during the growth process or not. Strong excitonic peaks with full width at half maximum of only 8 meV were observed in 4.2 K photoluminescence spectra of undoped Al 0.2 Ga 0.8 As layers grown at substrate temperatures as low as 550°C using As 4 . The epitaxial layers grown since the introduction of iodine are the brightest Al 0.2 Ga 0.8 As samples that we have obtained from our molecular beam epitaxy system. These results suggest that the presence of iodine in a molecular beam epitaxy system can result in improved optical properties for AlGaAs. The 4.2 K photoluminescence spectra and secondary ion mass spectroscopy depth profiles also show that iodine preferentially removes Ga from AlGaAs layers during growth, resulting in layers with higher Al content.

Combined silicon, beryllium, and carbon tetrabromide single-port dopant source for molecular-beam epitaxy

We report the design and the performance of a compact dopant source that combines silicon, beryllium, and carbon tetrabromide in a single port of a molecular-beam-epitaxy system. This design relies on the rapid thermal response of the silicon and beryllium source materials and the rapid response to valve operation of the carbon tetrabromide flux to form abrupt junctions, rather than on shuttering. It features disks of silicon and beryllium without crucibles for low thermal mass and rapid radiative heating and cooling, thermocouples riveted directly to the disks for accurate temperature tracking, and a water-cooled molybdenum baffle to isolate the silicon and beryllium cells. Secondary ion mass spectroscopy analysis of dopant profiles and the I–V characteristics of GaAs p–n junction diodes indicate negligible dopant overlap in Be/Si p–n junctions made without the use of a shutter. Doping density for silicon and beryllium in GaAs varied less than 3% across the central 56 mm diam of a 76 mm (3 in.) wafer. We...

Incorporation of thallium in InTlAs and GaTlAs grown by molecular beam epitaxy

Thallium incorporation in GaTlAs and InTlAs was systematically studied in solid source MBE by RHEED, Auger Electron Spectroscopy and X-ray diffraction as function of thallium concentration, substrate temperature and III/V flux ratio. Low temperature growth exhibits a (2/spl times/2) thallium-induced structure and also shows surface thallium accumulation. No evidence of binary TlAs formation was found. Auger electron spectroscopy measurements show limited thallium solubility in GaTlAs and InTlAs. X-ray diffraction measurements show the successful growth of epitaxial layers of TlGaAs with a molar fraction of Tl-0.5 and a second metal phase on the surface.