Fukunobu Osaka

Impact ionization coefficients of electrons and holes in

The arsenic composition dependences of electron and hole ionization coefficients, α and β, in

Excess noise design of InP/GaInAsP/GaInAs avalanche photodiodes

An InP/GaInAsP/GaInAs avalanche photodiode (APD) with separate absorption and multiplication (SAM) regions has been designed taking into account the excess noise generated in GaInAsP and GaInAs. The multiplication factor dependence of the excess noise factor F has been calculated using realistic electron and hole ionization rates in InP, GaInAsP, and GaInAs, assuming that the avalanche multiplication occurs not only in InP but in GaInAsP and GaInAs. The calculated F values have been compared to the experimental ones measured on a planar-type InP/GaInAsP/GaInAs APD for illumination at a wavelength of 1.3 μm. It has been found the the calculated excess noise agrees very well with the experimental measurements. The limited ranges of device parameters in which the conditions of minimal excess noise, tunneling current, and charge pile-up are satisfied have been obtained. We conclude that the excess noise generated in GaInAsP and GaInAs should be considered in a practical device design.

Electron and hole impact ionization rates in InP/Ga 0.47 In 0.53 As superlattice

The electron and hole impact ionization rates, α andβ, in an InP/Ga 0.47 In 0.53 As superlattice have been experimentally determined from photomultiplication data made on an InP/GaInAs superlattice photodiode. A Monte Carlo simulation of α and β in the superlattice has been developed, and the enhancement of impact ionization due to the effect of the band edge discontinuity has been investigated. The experimental ionization rates have been analyzed by the simulation. The larger β than α in the superlattice has been shown to be explained by the valence band discontinuity about two times larger than the conduction band edge discontinuity in this superlattice structure.

Scanning tunneling microscopy of molecular‐beam epitaxially grown GaAs (001) surfaces

A multichamber ultrahigh vacuum (UHV) scanning tunneling microscope (STM) system which includes a molecular‐beam epitaxy (MBE) growth chamber, as well as a STM chamber, has been constructed for the investigation of processed GaAs surfaces. We observed MBE‐grown GaAs surfaces using this system. Samples were grown on GaAs (001) surfaces and cooled to certain temperatures in an As4 flux before being transferred into an UHV. STM images of c(4×4), 2×4, and mixed c(4×2) and 2×2 structures were obtained for the samples cooled to 330, 570, and 470 °C in an As4 flux, respectively. The mixed c(4×2) and 2×2 structure seems to be formed by desorption of As atoms from the c(4×4) surface in an UHV. Also, a new reconstructed structure which has a 2.8‐nm periodicity along both the [110] and [110] directions was observed. It seems to be a local structure which has a larger arsenic dimer density than that of the c(4×4) structure.

Observation of Ga0.47In0.53As/InP multiquantum well structure in air by scanning tunneling microscope

A cross-sectional surface of Ga0.47In0.53As/InP multiquantum wells (MQWs) prepared by cleaving was observed in air by a scanning tunneling microscope (STM), and clear STM images of periodic MQW structures were obtained with nanometer resolution. The apparent height of the STM images on the surface of the GaInAs layers was 50–150 A larger than that of the images on the surface of the InP layers. This difference between the two kinds of layers was found to be due not to a real corrugation but to some difference in surface electronic properties. It was demonstrated that STM is a useful tool for nanometer scale evaluation of fine structures of MQWs.

Observation of multiquantum well structure in air using a scanning tunneling microscope

We investigated GaInAs/InP and AlAs/GaAs multiquantum well (MQW) structures in air using a scanning tunneling microscope (STM). We obtained clear corrugated images of MQWs with nanometer resolution. These corrugations come not from a topological difference but from the difference between the tunneling conductance of the well layers to the tip and that of the barrier layers to the tip. Also the STM images are affected by various factors such as contamination and humidity in the air. We observed degradation of the STM images which might be due to the surface oxidation accelerated by the tunneling current. The degradation rate of the AlAs/GaAs MQWs was much larger than that of the GaInAs/InP MQWs. This phenomenon is interesting from the viewpoint of nanometer scale processing.

Scanning Tunneling Microscopy of Ga0.47In0.53As/InP Multiquantum Well Structures in Air

Scanning tunneling microscope (STM) images of Ga0.47In0.53As/InP multiquantum well (MQW) structures in air showed a corrugated pattern. This corrugation turned out to be not geometrical but rather to arise from a difference in tunneling conductance between the GaInAs and the InP layers. The amplitude of the corrugations was affected by various factors such as contamination and atmospheric humidity.

Multiplication noise in planar InP/InGaAsP heterostructure avalanche photodiodes

Planar InP/InGaAsP avalanche photodiodes have been fabricated and multiplication noise is discussed. The effective hole to electron ionization rate ratio is found to be 1.9 from the wavelength dependence of multiplication noise.

Electron and hole ionization coefficients in (100) oriented Ga0.18In0.82As0.39P0.61

The impact ionization coefficients for electrons and holes in (100) oriented Ga0.18In0.82As0.39P0.61 whose band gap is 1.11 eV have been obtained from photomultiplication measurements on a Cd diffused p+n abrupt junction having a donor concentration of 2.5×1016 cm−3. The electron‐to‐hole ionization coefficient ratio has been found to be about 1.1 in the electric field range 4.0×105–5.0×105 V/cm.

Scanning tunneling microscopy of thermally cleaned InP surfaces in an arsenic flux

Abstract Thermally cleaned InP surfaces in an arsenic flux have been observed using an ultra-high-vacuum scanning tunneling microscope (UHV-STM). The STM image of the reconstructed In-stabilized surface showed 1.6 nm periodic lines in the [110] direction. The width of these lines was about 0.8 nm, each line comprising two rows when the sample was heated at 510°C for about one minute in an arsenic flux. On the other hand, the lines were about 0.4 nm wide and comprised a single row when the sample was heated at a higher temperature for a longer time. This result suggests that the In-stabilized surface comprises one or two In-In dimers and missing dimers per 4 × 2 cell, and that the dimer density depends on the cleaning conditions. For samples annealed at 480°C in a vacuum of 10 −5 Pa for about ten minutes after cleaning, the surface image showed 4 × 2 In-stabilized domains and 2 × 4 As-stabilized domains. This structure is thought to be formed by a desorption of surface atoms during annealing.