M.J. Hafich

Band offset of GaAs/In0.48Ga0.52P measured under hydrostatic pressure

Low‐temperature photoluminescence spectra of an In0.48Ga0.52P alloy and a p‐type GaAs/In0.48Ga0.52P multiple quantum well, both grown by molecular beam epitaxy, have been obtained under hydrostatic pressures from 0 to 6 GPa. The zero‐pressure extrapolation of the InGaP(X) to GaAs(Γ) transitions yields a 0.40±0.02 valence‐band offset, and hence only a small, 0.06 ± 0.02 eV, conduction‐band offset. These offset values are in agreement with measured values of the confinement energy versus well width.

High quality quantum wells of InGaP/GaAs grown by molecular beam epitaxy

High quality quantum wells of GaAs confined by barriers of InGaP have been grown by gas‐source molecular beam epitaxy. High‐resolution lattice images obtained with transmission electron microscopy of single quantum wells reveal high quality interfaces for both the normal InGaP/GaAs and the inverted GaAs/InGaP interface. Multiple‐line low‐temperature photoluminescence emission is observed for the thinnest GaAs quantum well. The range of well thicknesses examined was 0.6–5.2 nm, with the smallest well producing a quantum confinement energy shift of over 410 meV, corresponding to photoluminescence emission at 640 nm (1.94 eV) from GaAs.

Internal photoemission and energy‐band offsets in GaAs‐GaInP p‐I‐N heterojunction photodiodes

Internal photoemission has been observed in GaAs‐Ga0.52In0.48P p‐I‐N heterojunction photodiodes grown by gas source molecular beam epitaxy. Threshold energies associated with this photocurrent mechanism have been accurately measured. Simple analysis provides a precise determination of the energy‐band discontinuities in this heterostructure material system. The results indicate a conduction‐band discontinuity of ΔEc=108±6 meV at room temperature.Internal photoemission has been observed in GaAs‐Ga0.52In0.48P p‐I‐N heterojunction photodiodes grown by gas source molecular beam epitaxy. Threshold energies associated with this photocurrent mechanism have been accurately measured. Simple analysis provides a precise determination of the energy‐band discontinuities in this heterostructure material system. The results indicate a conduction‐band discontinuity of ΔEc=108±6 meV at room temperature.

Ultrafast graded double‐heterostructure GaInAs/InP photodiode

Ultrafast graded double‐heterostructure GaInAs/InP p‐i‐n photodiodes grown by gas source molecular beam epitaxy have been fabricated on an InP semi‐insulating substrate. The graded band‐gap layers and the double heterostructure reduce carrier trapping effects and diffusion current and the resulting response of a 5 μm×5 μm device was measured by electro‐optic sampling to be 5 ps full width at half maximum (FWHM). The deconvolved impulse response is 3.8 ps FWHM.

Growth of InP on Si substrates by molecular beam epitaxy

The growth of single‐crystal InP films on (100) Si substrates by molecular beam epitaxy (MBE) is described. Three different buffer layers were grown by gas‐source MBE in order to reduce the density of dislocations created by the 8% InP‐Si lattice mismatch. Double‐crystal x‐ray diffraction revealed that all buffer layers produced large‐area single‐crystal (100) InP films with the InP lattice tilted towards the 〈100〉 Si directions. A buffer layer of four Inx Ga1−x P/Iny Ga1−y P strained superlattices produced a specular InP film with an estimated dislocation density of 108–109 cm−2 and a residual stress of less than 5×10−4.

Electrical and optical feedback in an InGaAs/InP light-amplifying optical switch (LAOS)

A circuit model for optical and electrical feedback has been developed to investigate the cause of negative differential resistance (NDR) switching in a series connected heterojunction phototransistor (HPT) light-emitting diode (LED) device. The model considers optical feedback from the light generated in the LED, electrical feedback from the holes thermally emitted over the LED cladding layer, nonlinear gain of the HPT, the Early effect, and leakage resistance. The analysis shows that either electrical or optical feedback can be the dominant cause for the NDR, depending upon their relative strengths. The NDR observed in the devices was caused primarily by electrical feedback since the optical feedback is weak. For low input power, avalanche breakdown appears to initiate the NDR in the devices although avalanching alone cannot cause NDR. >

TEM study of the effect of growth interruption in MBE of InGaP/GaAs superlattices

The influence of growth interruption during the MBE growth of (100) In0.5Ga0.5P/GaAs superlattices is investigated by cross-sectional TEM. A roughening of the growth front is observed during an interruption after the exchange of the group-V molecular beams. The roughening of growth front occurs due to a spontaneous change in the growth orientation of the superlattice from [100] to 〈311〉 directions. This change in growth orientation is characterized by an initial formation of V-shaped grooves with {311} facets on the GaAs growth front which eventually lead to the formation of regions of {311} superlattice structures. The direction of V-shaped grooves is along the [011] axis, which is parallel to the surface dangling bonds of the group V atoms in the unreconstructed (100) plane. The most critical stage for the spontaneous change of the growth orientation is the interruption after the growth of a GaAs layer with the P2 flux.

The effect of growth pause on the composition of InGaP/GaAs Heterointerfaces

Abstract Molecular beam epitaxial (MBE) growth of InGaP/GaAs quantum-well structures requires switching of the arsenic and phosphorus molecular beams at each heterointerface. Using in-situ reflection high energy electron diffraction and ex-situ X-ray diffraction, the effects of a growth pause on the interfacial abruptness and composition during gas-source MBE growth of InGaP/GaAs superlattices were determined. Under conditions of a smooth growth front, the InGaP-to-GaAs and GaAs-to-InGaP interfaces were found to contain well-defined, thin regions of altered growth-V composition. For long pause times, the growth front became rough and the superlattice exhibited random fluctuations in layer thickness.

Quantum‐well structures of InAlP/InGaP grown by gas‐source molecular‐beam epitaxy

Both single quantum‐well (SQW) and multiple quantum‐well (MQW) structures have been produced using the technique of gas‐source molecular‐beam epitaxy to grow the two wide band‐gap ternary alloys, InAlP and InGaP. SQWs as narrow as two monolayers observed by bright field Transmission Electron Microscopy were found to be laterally uniform with abrupt InAlP/InGaP interfaces. Photoluminescence of SQWs of differing thickness produced a larger quantum confinement energy shift than expected, with emission at 570 nm for an InGaP well of 3.0 nm in thickness. The number and amplitude of peaks detected in double‐crystal x‐ray diffraction (DCXR) measurements of the MQW samples matched, to within the limit of the dynamic range of the DCXR system, the peaks calculated in a periodic two‐layer dynamical simulation of the x‐ray rocking curve.

Integrated optical NOR gate

A two-input optical NOR gate structure is proposed and demonstrated. The NOR gate is fabricated from a vertically integrated heterojunction phototransistor and light emitting diode InGaAs-InP structure grown by gas source molecular beam epitaxy. Operation up to 500 kHz is demonstrated for devices fabricated with 250- mu m*250- mu m mesas. Analysis indicates that operation at frequencies up to 50-100 MHz is possible for smaller mesa areas. ON/OFF optical contrast ratios as high as 30 were measured.<<ETX>>