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.

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

We report in situ etching in III-V molecular beam epitaxy (MBE) with AsBr3 as the etching species and MBE regrowth of in situ structured GaAs substrates. The application of AsBr3 provides atomic layer precise etching as well as full compatibility with MBE growth. The quality of etched interfaces in GaAs/AlGaAs heterostructures is investigated by photoluminescence (PL) and Hall-effect measurements. They indicate a slightly enhanced interface roughness for etched samples compared to as-grown structures but no incorporation of bromine could be detected. However, an insufficient removal of dopants as well as carbon and oxygen surface contamination was observed in SIMS studies. A material selectivity between the metallic components In, Ga and Al was investigated as well as a crystallographic selectivity in GaAs. Selective etching of SiO2 masked GaAs(100) substrates allows in situ preparation of extremely sharp V-grooves with almost perfectly planar {110} side facets. By MBE regrowth of V-grooves we prepared buried layers and completely embedded wires which were characterized by SEM and PL.

http://iopscience.iop.org/article/10.1088/0268-1242/15/2/316/pdf

In situ etching with AsBr3 and regrowth in molecular beam epitaxy

This thesis deals with the development of high speed InPmesa HBTs with power gain cutoff frequencies up toand above 300 GHz, with high current density and low collectordischarging times.Key developments are Pdbased base ohmics yielding basecontact resistances as low as 10 Ωµm2, basecollector grades to enable to use ofInP in the collector, and an increase in the maximum currentdensity through collector design and thermal optimization.HBTs with a linear doping gradient in the base are forthe first time reported and compared to HBTs with abandgap graded base. The effect of degenerate base doping issimulated, as well as the base transit time.Key results include a DHBT with a 215 nm thick collector andan fτ= 280GHz, and fmax=400 GHz. This represents the highest fmaxreported for a mesa HBT. Results also include aDHBT with a 150 nm thick collector and an fτ= 300 GHz, and fmax=280 GHz. The maximum operating current densityhas been increased to above 10 mAµm while maintaining fτand fmax≥ 200 GHz.A mesa DHBT process with and as much yield and simplicity aspossible has been developed, while maintaining or pushingworldclass performance.

Ultra High Speed InP Heterojunction Bipolar Transistors

Atomic layer in situ etching and MBE regrowth

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High-Speed InP Heterojunction Bipolar Transistors and Integrated Circuits in Transferred Substrate Technology

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.

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

We demonstrate that high-quality lattice-mismatched In0.73Ga0.27As:InP photodetectors for use at 2.2 μm can be grown by molecular beam epitaxy using compositionally graded buffer layers. By investigating various growth conditions, we found that the quality of the active layer material depends on the thickness of the compositionally graded buffer layers and the substrate temperature during the growth of the compositionally graded buffer layers and active layers. The best device performance was obtained from a sample with a 1.0 μm compositionally graded buffer grown at a substrate temperature of 350 °C combined with active layers grown at 400 °C. The typical room temperature dark current at a reverse bias of 1 V for 100×100 μm2 photodetectors on this sample was 2 mA/cm2. This dark current is a factor of 10 better than that of commercially available devices fabricated from material grown using vapor phase epitaxy.

Molecular beam epitaxy of highly mismatched In0.73Ga0.27As on InP for near-infrared photodetectors

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...

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

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%.

M. Micovic

Papers

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

Molecular beam epitaxy of highly mismatched In0.73Ga0.27As on InP for near-infrared photodetectors

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

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