Molecular beam epitaxy is an ultrahigh vacuum technique for growing very thin epitaxial layers of semiconductor crystals. Because it is inherently a slow growth process, extreme dimensional control over both major compositional variations and impurity incorporation can be achieved. The result is that it has been possible, with one combination of lattice-matched semiconductors, GaAs and Al x -Ga l– x As, to demonstrate a large variety of novel single-crystal structures. These results have important implications for fundamental studies of the physics of thin-layered structures and for the development of new semiconductor electronic and optoelectronic devices.

https://science.sciencemag.org/content/sci/208/4446/916.full.pdf

Molecular beam epitaxy.

Small‐area (≲1 μm2) oxide‐barrier tunnel junctions have been made of thermally cyclable superconducting Pb alloys for use as high‐frequency mixers. A single‐sideband mixer noise temperature of <100 K has been achieved at 115 GHz. This result was achieved in the quasiparticle (classical) mixing mode.

Low-noise 115-GHz mixing in superconducting oxide-barrier tunnel junctions

The two-diode subharmonically pumped stripline mixer has a pair of diodes shunt mounted with opposite polarities in a stripline circuit between the signal and local oscillator inputs. The circuit has low noise and conversion loss and substantial AM local oscillator noise cancellation.The local oscillator frequency is about half the signal frequency. A novel diode chip, the notch-front diode, which has ohmic contacts on the chip faces adjacent the face containing the diode junctions, was developed for these circuits. The notch-front diode permits the low parasitic reactance of the waveguide diode mount to be achieved in stripline circuits. The best performance for a two-diode subharmonically pumped mixer with notch-front diodes was a 400 K mixer noise temperature, obtained at 98 GHz which is comparable to the best fundamental mixers in this frequency range. The performance over a 47-110-GHz frequency range for this circuit with commercial beam-lead diodes is also presented.

Subharmonically Pumped Millimeter-Wave Mixers

Growth temperature dependence in molecular beam epitaxy of gallium arsenide

Integrated optics and integrated microwave circuits require extremely uniform epitaxial layer thicknesses, composition profiles, and doping profiles. With a sample rotating mechanism, molecular beam epitaxy can for the first time prepare GaAs and AlxGa1−xAs layers with thickness variation of less than 1% over a lateral dimension of 5 cm. The variation of AlAs mole fraction of the Al0.3Ga0.7As over a 10‐cm2 area was less than 0.4%. The variation of the ’’pinch‐off’’ voltage for a field effect transistor structure was less than 1.4% over a 10‐cm2 wafer. These results represent the most uniform epitaxial layers ever prepared with any crystal growth technology.

Growth of extremely uniform layers by rotating substrate holder with molecular beam epitaxy for applications to electro-optic and microwave devices

Schottky barrier diodes which are specifically designed for use in cryogenically cooled millimeter‐wave mixers have been fabricated from MBE layers grown on heavily doped GaAs substrates. At 15 K the devices show a nearly exponential current‐voltage characteristic and a diode noise temperature which is determined predominantly by the tunneling transport mechanism. A diode noise temperature as low as 55 K was achieved under pumped conditions. This is the lowest diode noise temperature ever obtained in a resistive mixer. A single sideband mixer noise temperature of 315 K was measured at 102 GHz for a cryogenic mixer employing these diodes.

M. V. Schneider

Papers

Low‐noise millimeter‐wave mixer diodes prepared by molecular beam epitaxy (MBE)