During the heteroepitaxy of Ge on GaAs, arsenic diffuses from the GaAs substrates and hence is present in the Ge epilayer. It has been shown that As is incorporated into the layer but also segregated to the surface. The Ge growth is monitored in situ by laser reflectometry, and it gives the thickness, the growth rate, and the morphology of the layer. It is shown here that a too large surface concentration of As due to intentional doping can block the Ge growth. Atomic force micrographs of the morphological defects (pyramidlike void and large steps) suggest that these defects are due to local segregated excess As concentrations caused by the step advance. It is shown that the density of defects as well as the thickness at which they appear are characterized by the same activation energy of ∼1 eV.

Role of arsenic in the heteroepitaxy of Ge/GaAs

Electrical characteristics ofp-Ge/n-GaAs heterojunctions on GaAs(l00) grown by molecular beam epitaxy (MBE) have been investigated. Thep-type Ge layer was produced by intentionally doping with Ga atoms, in addition to the diffusion of Ga atoms from the surface of the GaAs layer. The best ideality factor of 1.04 over six decades of the forward current and the lowest reverse current density of the order of 10−6 A/cm2 were obtained for diodes with Ge grown at 500° C. The ideality factor increased slightly up to 1.12 when the operating temperature was decreased to 77 K. By studying the temperature dependence of the forward current, the conduction band discontinuity has been estimated to be 40 ± 10 meV. The suppression of Ga diffusion into the Ge film and its effect on pn-junction characteristics were also studied by growing a thin Ge film on GaAs at less than 300° C prior to the normal Ge film growth at 500° C.

https://link.springer.com/content/pdf/10.1007/BF02651281.pdf

Current-voltage characteristics of p -Ge/n-GaAs heterojunction diodes grown by molecular beam epitaxy

A compound semiconductor integrated circuit device has a region implanted with an impurity for forming a carrier capture level in an element isolating region in a semi-insulating compound semiconductor substrate. The region includes at least a first region of relatively low implantation concentration of the impurity and a second region of relatively high implantation concentration of the impurity.

Compound semiconductor integrated circuit device with an element isolating region

A heterostructure bipolar transistor is formed by a process of steps of holding an N-type gallium arsenide body using as an emitter region in a high vacuum of 10-9 torr to 10-13 torr at a first temperature of 400° C. to 1,000° C. where arsenic on a surface of the gallium arsenide body drifts away, lowering the first temperature to a second temperature of 300° C. to 400° C. to start a molecular beam epitaxial growth of a germanium, and forming an N-type germanium layer using as a collector region.

Method for manufacturing a heterostructure transistor having a germanium layer on gallium arsenide using molecular beam epitaxial growth

GeAs is successfully applied as a new arsenic dimer source for efficient n‐type doping of Ge grown by molecular beam epitaxy. The arsenic fluxes emanating from GeAs Knudsen cells are not composed of arsenic tetramers, but only of arsenic dimers. High electron concentrations of up to 1.1×1020 cm−3 are achieved with GeAs, which is much larger than any ever obtained in antimony‐doped Ge. The electron concentration in the arsenic‐doped Ge films depends on the GeAs cell temperature with an activation energy of 2.5 eV, which coincides with that of the arsenic dimer beam flux generated from GeAs. Moreover, it is found that the electron and arsenic concentrations in the arsenic‐doped Ge layer are identical. These results indicate that arsenic atoms are incorporated into Ge from the arsenic dimer beam, and that a very high electrical activation of the incorporated arsenic atoms is obtained.

GeAs as a novel arsenic dimer source for n‐type doping of Ge grown by molecular beam epitaxy

We have investigated the limitation of the active area of p‐n Ge/GaAs heterojunctions by means of B ion implantation into the interface of Ge/GaAs structure. Germanium epilayers were grown on (100) GaAs substrates by molecular beam epitaxy at a substrate temperature above 450 °C with a growth rate of about 10 nm/min. The Ge/GaAs heterojunction diode, fabricated with p‐n Ge/GaAs structure which was grown at the substrate temperature of 500 °C, represented a forward current voltage shoulder of 0.44 V and a breakdown voltage of 44 V. The ideality factor and the backward step recovery time of this diode was 1.09 and about 10 ns, respectively, similar to a Schottky barrier diode with same active area. In order to use the n‐GaAs substrate as an emitter of a heterobipolar transistor, it is necessary to limit the current flow into the same area of the collector through the base region. To realize this idea, B ions were implanted through the Ge epilayer, and the high‐resistivity region was formed in the GaAs subst...

T. Itoh

Papers

Active area limitation of Ge/GaAs heterojunctions by means of B ion implantation