J.R. Hayes

Lateral and longitudinal patterning of semiconductor structures by crystal growth on nonplanar and dielectric-masked GaAs substrates : application to thickness-modulated waveguide structures

Abstract Two methods which achieve both lateral and longitudinal patterning of semiconductor properties by organometallic chemical vapor deposition (OMCVD) are presented. Both approaches utilize diffusion of reactant species from a nongrowth surface to an adjacent growth surface, presumably via the gas phase. In the first method, the nongrowth surface is the (111)B facet which develops during deposition on a GaAs substrate where mesas in the (011) orientation have been etched prior to growth. Low-loss single mode rib-type waveguides (0.6 dB/cm at 1.52 μm wavelength) were fabricated with this approach. In the second method, the nongrowth surface is a dielectric mask deposited on the GaAs surface prior to growth. Growth rate enhancements can be controlled, and can be as high as 280% with this second approach, which appears to be more practical than the first one. This new capability for OMCVD will offer a wide range of applications.

Etching of InP by HCl in an OMVPE reactor

Abstract We investigated etching of (100) InP by HCl gas inside an OMVPE reactor, at 76 Torr, and at temperatures of 580 or 625°C. Proper choice of etching parameters led to very good (at 625°C) of fair (at 580°C) morphologies for etched depths of up to 3μm. With SiO 2 stripes or stripe openings on the (100) surface, ridges or V grooves were obtained by etching, limited by very smooth (111) A or (111) B walls.

Quantum interference effects in GaAs/GaAlAs bulk potential barriers

We have observed a large number of oscillations (10) in the current/voltage characteristic of GaAs/GaAlAs triangular potential barriers due to quantum interference effects. When an exact number of periods of a standing wave is present in the barrier there is a minimum in the transmission coefficient for electrons. As the bias is changed the electron wavelength is changed and there will once again be a minimum when the next complete period of the standing wave is incorporated. The observation of this quantum interference effect enables us to conclude that the scattering rate for hot electrons, high in the energy band of GaAs, is much less than previously assumed.

‘‘Ballistic’’ injection devices in semiconductors

‘‘Ballistic’’ electron transistors are of considerable interest for high‐frequency operation. Regardless of the mechanism of electron injection or collection it is anticipated that device performance will be dominated by base transit dynamics. We address this issue by calculating the scattering rate for hot electrons in selected semiconductor materials holding some common band structure and transport properties. It is shown that the scattering rate is critically dependent on the carrier concentration and that GaAs is not suitable for fabrication of traditional ‘‘ballistic’’ electron transistors. We suggest that semiconductors with small effective electron mass or a two‐dimensional system would be more suitable.

Base transport dynamics in a heterojunction bipolar transistor

We have used hot‐electron spectroscopy to study nonequilibrium electron transport in the base of a heterojunction bipolar transistor. Electrons injected from an n‐type AlGaAs emitter into a p‐type GaAs base were found to be strongly scattered such that they could be characterized by an effective electron temperature after traversing several hundred angstroms. The effective electron temperature, measured at 4.2 K, was found to be 150 K for a sample having a 900‐A base region and 500 K for a sample having a 450‐A base region.

Tunnel injection into a Wannier–Stark ladder

We describe tunneling measurements of the electronic states of superlattices in which an electric field has destroyed the miniband structure. The tunneling characteristics reveal that the minibands collapse into localized Wannier–Stark states, which can be resolved in the first two quantum wells of the superlattice. The positions can be accounted for quantitatively by a combination of electrostatic and quantum mechanical effects.

Electroluminescence from the base of a GaAs/AlGaAs double heterojunction bipolar transistor

We have measured the electroluminescence spectrum of a double heterojunction bipolar transistor and found that a potential well formed at the base‐collector junction acts as a preferential trap of low‐energy electrons in the base. At high injection current densities the trap saturates. The subsequent buildup of carriers in the base changes the transistor turn‐on characteristics.

Resonant tunneling in crossed electric and magnetic fields

A wide (80 nm) double‐barrier resonant tunneling structure shows 25 features in the current‐voltage characteristic associated with resonances in the quantum well. When a transverse magnetic field is applied to the structure, the features weaken and shift to higher energies. We give a quantum mechanical description of this phenomenon which is able to account quantitatively for the magnitude of the shifts.

Hot electron spectroscopy of GaAs

Abstract We report results both experimental and theoretical on the dynamics of hot electron transport in GaAs. Total elastic and inelastic scattering rates are calculated and compared with the results of a new experimental technique “Hot Electron Spectroscopy”. The magnetic field dependence of hot electron spectra has been studied. It is shown that application of a magnetic field normal the injection direction has a dramatic effect on the spectra whereas a magnetic field applied parallel to the injection direction has no effect. The magnetic field is shown to increase the effective transit region width of the spectrometer enabling us to obtain a scattering rate for hot electrons. The experimentally determined rate gives good agreement with a theoretically determined rate considering scattering by coupled plasmon/phonon modes.

Tunneling measurement of the density of states of a superlattice

We have studied the current‐voltage characteristics of GaAs/AlGaAs samples consisting of an electron injector, a wide AlGaAs tunnel barrier, and a strongly coupled superlattice. The bias determines the energy of electrons injected into the superlattice, and the resulting tunnel current shows pronounced structure associated with minibands and band gaps. The position of the bands is in quantitative agreement with theory, and we resolve minibands with energies both below and above the AlGaAs conduction‐band offset.