Archie L. Holmes

InGaAs/InAlAs avalanche photodiode with undepleted absorber

We report an avalanche photodiode with an undepleted p-type InGaAs absorption region and a thin InAlAs multiplication layer. The motivation for utilizing an undepleted absorption layer, which is similar to that in the unitraveling carrier photodiode, is to reduce the dark current. A dark current below 1 nA at a gain of 10 and a gain–bandwidth product of 160 GHz are demonstrated.

Breakdown voltage in thin III–V avalanche photodiodes

The dead-space multiplication theory of Hayat and Saleh [J. Lightwave Technol. 10, 1415 (1992)], in conjunction with the multiplication-width-independent ionization-coefficient model developed by Saleh et al. [IEEE Trans. Electron Devices 47, 625 (2000)], are shown to accurately predict breakdown voltages for thin avalanche photodiodes of GaAs, InP, In0.52Al0.48As, and Al0.2Ga0.8As, over a broad range of device widths. The breakdown voltage is determined from the analytical expression for the impulse-response-function decay rate.

Growth of GaNAs by molecular beam expitaxy using a N2/Ar rf plasma

A high efficiency nitrogen rf plasma source has been used to grow GaNAs by diluting the N2 gas with Ar. This source (an EPI UniBulb™ source) was originally designed for use in the growth of pure nitrides at high growth rates. For growth of As-rich GaNAs, high concentrations of active nitrogen lead to the growth of GaN instead of a random alloy. In this work we demonstrate that a dilute N2/Ar mixture leads to GaNAs films where the amount of nitrogen incorporation varies directly with the percentage of N2 in the gas mixture. Films with high structural quality were grown, thus validating the use of this approach.A high efficiency nitrogen rf plasma source has been used to grow GaNAs by diluting the N2 gas with Ar. This source (an EPI UniBulb™ source) was originally designed for use in the growth of pure nitrides at high growth rates. For growth of As-rich GaNAs, high concentrations of active nitrogen lead to the growth of GaN instead of a random alloy. In this work we demonstrate that a dilute N2/Ar mixture leads to GaNAs films where the amount of nitrogen incorporation varies directly with the percentage of N2 in the gas mixture. Films with high structural quality were grown, thus validating the use of this approach.

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...

Ion damage effects from negative deflector plate voltages during the plasma-assisted molecular-beam epitaxy growth of dilute nitrides

We studied the effects of ion damage on the optical properties of dilute nitrides grown by plasma-assisted molecular-beam epitaxy. A dual-grid retarding field ion energy analyzer was used to measure the ion flux and ion energy distribution at the substrate position from an Applied-EPI UniBuilb™ rf plasma cell. These changes were measured as the negative deflector plate voltage varied from 0 to −800V. The largest ion flux resulted with a −100V setting, while the greatest ion energies occurred with −200V. Deflector plate voltages more negative than −300V resulted in a significant reduction in both the ion flux and ion energy. The damage caused by these ions was determined by measuring the pre- and postanneal photoluminescence properties of Ga0.8In0.2N0.01As0.99 quantum wells. Comparable optical properties were possible with various combinations of ion fluxes and ion energies, which demonstrate how the ion flux and ion energy each impart an individual effect on the sample’s optical properties. An awareness o...

Diffusion mechanisms of indium and nitrogen during the annealing of InGaAs quantum wells with GaNAs barriers and GaAs spacer layers

In this article, we discuss two indium diffusion mechanisms that are present during the rapid thermal annealing of InxGa1−xAs quantum wells (x=0.18, 0.22, and 0.26) with GaNyAs1−y barriers (y=0.6 or 1.2%). Samples were grown with and without a GaAs spacer layer in between the quantum well and barrier. The dominant mechanism is dependent on the amount of thermal energy applied during the annealing process. At low annealing times and temperatures, we have observed that In-Ga intra-diffusion entirely within the quantum well is dominant. For the higher times and temperatures, In-Ga inter-diffusion between the quantum well and barrier becomes dominant. These observations were confirmed by high-resolution x-ray diffraction and the peak emission wavelengths were measured by room-temperature photoluminescence. We have also observed that nitrogen had diffused from the GaNAs barriers into the InGaAs quantum wells in all of our annealed samples. In addition, the commonly observed indium-content dependent diffusion i...

Low-temperature breakdown properties of AlxGa1−xAs avalanche photodiodes

AlxGa1−xAs (x=0.0–0.9) homojunction avalanche photodiodes are characterized in the temperature range of 11–300 K. For all compositions, the breakdown electric field strength decreases with temperature, and the rate of change is smaller at temperatures below 50 K than at higher temperatures. This results from the fact that spontaneous phonon emission dominates carrier scattering in the 0 K limit. The rate of change of the breakdown field strength is smallest for Al0.6Ga0.4As compared with other compositions. This is likely due to higher alloy scattering at x=0.6. A Monte Carlo model that provides good fits to experimental data is presented.

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...

Construction of a variable aperture cell for source flux control in a molecular-beam epitaxy environment

A molecular-beam source utilizing instant flux adjustment for growth rate control is presented. The design uses a two-filament pyrolytic boron nitride (pBN) heater constructed with eight heated exit aperture holes, masked by an aperture-mating pBN closed end cylinder. The rotatable pBN mask opens and closes the effusion cell apertures to provide mechanical control of the source flux. This adjustment is provided by a rotational manipulator that translates rotary motion through the vacuum environment to the mounting journal of the pBN mask cylinder. RHEED oscillation changes in GaAs homoepitaxial growth shows an effectively instantaneous change of nearly an order of magnitude in the growth rate.

Growth and characterization of Ga0.8In0.2(N)As quantum wells with GaNxAs1−x(x⩽0.05) barriers by plasma-assisted molecular beam epitaxy

GaInNAs has received significant attention due to the ability to achieve 1300 nm wavelengths on GaAs substrates. In most cases, nitrogen is added directly into the GaInAs quantum wells, which degrades their optical properties. In this work, we investigate how the placement of nitrogen in Ga0.8In0.2As/GaAs heterostructures affects their optical characteristics. The location of nitrogen was studied in three different structures: nitrogen in barriers alone, nitrogen in wells alone, and nitrogen in the wells and barriers. Our results show that placing nitrogen in the barriers instead of wells provides better luminescence properties. We also observed that the addition of a GaAs spacer at the barrier-well interfaces further improves the luminescence properties of the structure.