J. B. Hurst

Molecular-beam epitaxy growth of device-compatible GaAs on silicon substrates with thin (∼80nm) Si1−xGex step-graded buffer layers for high-κ III-V metal-oxide-semiconductor field effect transistor applications

The authors report the fabrication of TaN–HfO2–GaAs metal-oxide-semiconductor capacitors on silicon substrates. GaAs was grown by migration-enhanced epitaxy (MEE) on Si substrates using an ∼80-nm-thick Si1−xGex step-graded buffer layer, which was grown by ultrahigh vacuum chemical vapor deposition. The MEE growth temperatures for GaAs were 375 and 400°C, with GaAs layer thicknesses of 15 and 30nm. We observed an optimal MEE growth condition at 400°C using a 30nm GaAs layer. Growth temperatures in excess of 400°C resulted in semiconductor surfaces rougher than 1nm rms, which were unsuitable for the subsequent deposition of a 6.5-nm-thick HfO2 gate dielectric. A minimum GaAs thickness of 30nm was necessary to obtain reasonable capacitance-voltage (C-V) characteristics from the GaAs layers grown on Si substrates. To improve the interface properties between HfO2 and GaAs, a thin 1.5nm Ge interfacial layer was grown by molecular-beam epitaxy in situ after the GaAs growth. The Ge-passivated GaAs samples were th...

Long-wavelength In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As large-area avalanche photodiodes and arrays

Large-area (500-/spl mu/m diameter) mesa-structure In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiodes (APDs) are reported. The dark current density was /spl sim/2.5/spl times/10/sup -2/ nA//spl mu/m/sup 2/ at 90% of breakdown; low surface leakage current density (/spl sim/4.2 pA//spl mu/m) was achieved with wet chemical etching and SiO/sub 2/ passivation. An 18 /spl times/ 18 APD array with uniform distributions of breakdown voltage, dark current, and multiplication gain has also been demonstrated. The APDs in the array achieved 3-dB bandwidth of /spl sim/8 GHz at low gain and a gain-bandwidth product of /spl sim/120 GHz.

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.

Unintentional Calcium Incorporation in Ga(Al, In, N)As

Unintentional calcium incorporation into GaInNAs causes an acceptor-type impurity, which limits the ability of ∼1eV GaInNAs-based solar cells to collect photogenerated current. Here, the authors focus on better understanding the conditions by which Ca is incorporated into GaInNAs. Various material combinations were grown including GaAs, InGaAs, GaInNAs, and Al(Ga)As. The materials were primarily grown by solid-source molecular-beam epitaxy (MBE) at ∼400 and 580–620°C, with comparisons made to metal-organic chemical vapor deposition (MOCVD)-grown materials where appropriate. Calcium incorporation was measured through secondary ion mass spectrometry. There was no measurable Ca incorporation into MBE-grown GaAs at 580°C, but Ca incorporates into GaAs at low MBE growth temperatures (∼400°C) that are comparable to those typically used for GaInNAs. This suggests that the N species is not solely responsible for the observed Ca incorporation into MBE-grown GaInNAs; but rather, defects associated with the low temp...

Photodetectors: UV to IR

This paper surveys recent work in several photodetector areas including high-speed, low-noise avalanche photodiodes, solar-blind ultra-violet PIN photodiodes, and quantum dot infrared photodetectors (QDIPs).

Atomic force microscopy study of sapphire surfaces annealed with a H2O flux from a baffled molecular-beam epitaxy effusion cell loaded with Al(OH)3

We present an atomic force microscopy (AFM) study of sapphire surfaces that contain scratches with various severities. The objective was to observe the effects of substrate annealing at 850°C for 200min with a H2O-based overpressure resulting from an Al(OH)3 powder that was thermally cracked at 1200°C. The Al(OH)3 was decomposed into Al2O3 and H2O according to a partial Bayer process in a modified molecular-beam epitaxy (MBE) effusion cell, which was equipped with homemade baffles placed at its outlet. These homemade, simple-to-construct tantalum baffles allow for the selective outfluxing of gaseous species, from those that are solid based. A UTI™ 100C-model mass spectrometer was used to monitor the species present at the sapphire surface during annealing. Any aluminum-based solid species from the Al(OH)3 were not observed in the mass spectrum, although the H2O-based species were. The sapphire substrates were annealed in a Varian Gen II™ MBE system, with H2O beam equivalent pressures (BEPs) of 5×10−6 and ...

Inert gas maintenance for molecular-beam epitaxy systems

Molecular-beam epitaxy (MBE) most often involves the use of highly toxic and combustible materials, which may subject maintenance personnel to increased health risks. In our efforts to reduce these hazards, we describe the use of inert gas maintenance equipment and procedures that can be employed during the opening of MBE growth chambers. Our operations involve the use of nitrogen-purged glovebags that are sealed over the open port of the growth chamber, wherein applicable tasks are performed through appropriate gloveports of the glovebag. We also describe the associated equipment utilized inside of the glovebags, which aid in the removal of the substrate manipulator and effusion cells. The benefits of reducing the exposure of air to the growth chamber are observed after a bakeout of 145h, wherein the AsO partial pressure within the growth chamber was a factor of 10 lower due to our inert gas maintenance procedures than without. The use of these glovebags allows us to both terminate our bakeout approximat...

Recent developments in avalanche photodiodes

This paper surveys recent work in several photodetector areas including high-speed, low-noise avalanche photodiodes, solar-blind ultra-violet PIN photodiodes, and quantum dot infrared photodetectors (QDIPs).