D. Lubyshev

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.

GaAs/AlGaAs heterojunction bipolar transistors with a base doping 1020 cm−3 grown by solid-source molecular beam epitaxy using CBr4

We show that epitaxial layers suitable for fabrication of AlGaAs/GaAs heterojunction bipolar transistors with a carbon base doping level of up to 1020 cm−3 can be grown by solid-source molecular beam epitaxy using CBr4 as a doping precursor. We have observed that the gain of devices fabricated from these layers is improved using an abrupt conduction-band discontinuity at the emitter–base heterointerface. The observed relationship between current gain and the base width Wb of these devices deviates from the 1/Wb2 dependence predicted by diffusive electron transport for base widths that are shorter than 60 nm. The relationship is better approximated by a 1/Wb dependence, which is in better agreement with the theories of ballistic or quasiballistic electron transport. Current gain of the devices drops rapidly as the base thickness exceeds 60 nm.

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.

The Effect of Al0.7Ga0.3As Etch Stop Removal on the Preparation of Wafer‐Bonded Compliant Substrates

Preparation of GaAs-based compliant substrates that utilize wafer bonding generally relies on integrated Al x Ga 1- x As etch stop layers to provide the precise control required to stop selectively on GaAs layers less than 100 A thick. We demonstrate that removing an Al 0.7 Ga 0.3 As etch stop layer with HF or HCl:H 2 O leaves the underlying GaAs layers with rms roughness of 10-20 A and peak-to-peak roughness of 65-150 A. Following the Al 0.7 Ga 0.3 As selective etch, the morphology of the underlying GaAs layer is improved with a wet chemical digital etch comprised of alternate soaks in H 2 O 2 and HCl:H 2 O, which results in a GaAs surface with rms roughness of ∼2 A and peak-to-peak roughness of ∼20 A. Lattice-matched p + -n junctions deposited on thin-bonded GaAs substrates and test substrates that are prepared for growth using the digital etch have electrical characteristics comparable to those deposited on a bulk epi-ready GaAs substrates. However, similar lattice-mismatched In 0.2 Ga 0.8 As p + -n junctions deposited on the thin-bonded GaAs substrates and test substrates have dark currents that are more than an order of magnitude higher than those deposited on bulk epi-ready GaAs substrates. These results suggest that despite the smoothing of the digital etch, the material that remains on the surface of the thin GaAs layer is responsible for the degradation observed in the lattice-mismatched devices deposited on the thin-bonded GaAs substrates.

Molecular beam epitaxial growth of InAs on a (311)A corrugated surface: Growth mechanism and morphology

Kinetic molecular beam epitaxy growth processes and the structure of the InAs (311)A surface were investigated in situ by reflection high energy electron diffraction (RHEED) and ex situ by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Two stable surface structures, (2×15) and (1×5), were observed by RHEED on as-grown surfaces. RHEED oscillations have a strong azimuthal anisotropy with maximum amplitude in the [233] direction and minimum amplitude in the [011] direction, suggesting that this surface grows via propagation and coalescence of pronounced two dimensional nuclei along the [233] azimuth. Ex situ LEED and STM studies of the As-capped InAs (311)A surfaces confirmed the strong anisotropy of the surface structure. A characteristic feature of the LEED patterns is the degeneration of the principal diffraction into streaks along the [011] direction. STM images show rows running along the [233] direction. Although the spacing between the rows varies, there are local...

Fabrication of heterojunction bipolar transistors with buried subcollector layers for reduction of base-collector capacitance by molecular beam epitaxy regrowth

A process for fabrication of heterojunction bipolar transistors (HBTs) with selectively buried subcollectors by molecular beam epitaxy (MBE) regrowth is described. This process can be used to reduce parasitic base-collector capacitance of HBTs and improve the speed of these devices. In situ etching by iodine prior to the regrowth was used for the first time to improve the quality of the substrate epilayer interface in a semiconductor device grown by MBE. The secondary ion mass spectroscopy depth profiles of regrown HBT structures suggest that the in situ surface cleaning by molecular iodine was not sufficient to remove all contamination from the substrate epilayer interface and that the microwave performance of HBTs fabricated by this process may have been affected by that contamination. The dc performance of devices which were fabricated by our process was not affected, however, by the contamination and was comparable to the dc performance of conventional HBTs. Our results suggest that the described proc...

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%.