M. W. Koch

Use of a valved, solid phosphorus source for the growth of Ga0.5In0.5P and Al0.5In0.5P by molecular beam epitaxy

We report on a new method for the generation of phosphorus beams in molecular beam epitaxy: the use of a valved, solid cracker source. The valved solid source avoids previous difficulties associated with the use of solid phosphorus, and provides an attractive alternative to the use of phosphine. The use of red phosphorus does not interfere with the subsequent growth of high quality arsenides in the same growth chamber. The performance of this valved phosphorus source is illustrated by the growth of two ternary phosphides, Ga0.5In0.5P and Al0.5In0.5P. The quality of the phosphides reported here is comparable to the best results reported by other growth techniques. The effects of composition, growth temperature, and P2 flux on the films’ characteristics are reported. Indium desorption during growth is found to be substantially greater in AlInP than in GaInP.

Colliding-pulse passive harmonic mode-locking in a femtosecond Yb-doped fiber laser with a semiconductor saturable absorber

We demonstrate a passive harmonic mode-locked femtosecond Yb-doped fiber laser employing a semiconductor saturable absorber in a colliding-pulse configuration. 380-fs pulses at 605 MHz repetition rate with >60 dB supermode suppression is achieved.

PHOSPHORUS-VACANCY-RELATED DEEP LEVELS IN GAINP LAYERS

Deep levels in lattice‐matched Ga0.51In0.49P/GaAs heterostructure have been investigated by thermal‐electric effect spectroscopy (TEES) and temperature‐dependent conductivity measurements. Four samples were grown by molecular‐beam epitaxy with various phosphorus (P2) beam‐equivalent pressures (BEP) of 0.125, 0.5, 2, and 4×10−4 Torr. A phosphorus vacancy (VP) ‐related deep level, an electron trap, was observed located at EC−0.28±0.02 eV. This trap dominated the conduction‐band conduction at T≳220 K and was responsible for the variable‐range hopping conduction when T<220 K. Its concentration decreased with the increasing phosphorous BEP. Successive rapid thermal annealing showed that its concentration increased with the increasing annealing temperature. Another electron trap at EC−0.51 eV was also observed only in samples with P2 BEP less than 2×10−4 Torr. Its capture cross section was 4.5×10−15 cm2. This trap is attributed to VP‐related complexes.

Molecular beam epitaxy growth of boron-containing nitrides

Layers of BN, BGaN and BAlN were grown by molecular beam epitaxy using ammonia on (0001) sapphire substrates. The crystal structure and material quality of these layers were assessed by reflection high energy electron diffraction, x-ray diffraction, Fourier transform infrared reflectance, and photoluminescence spectroscopy. These measurements reveal that while BN layers grow as polycrystalline films, BGaN and BAlN layers grow as single crystals with boron composition up to 2% and 6%, respectively. A monotonic increase in the band gap energy and a decrease in c-lattice constant were observed with increasing boron concentrations in BGaN samples. Yellow-band emission and increased surface roughening were also observed in samples with higher boron compositions.

GaInP and AlInP grown by elemental source molecular beam epitaxy

We report on the use of a new, valved, solid phosphorus cracker source for the growth of phosphides by molecular beam epitaxy. The source avoids the relatively high expense and high level of toxicity associated with the use of phosphine gas and eliminates the problems commonly encountered in using conventional solid phosphorus sources. The source has been used to grow GaInP and AlInP lattice-matched to GaAs substrates. The quality of the materials reported here is comparable to the best materials grown by other techniques. Photoluminescence and Raman scattering measurements indicate that the resulting material has a high degree of disorder on the group III sublattice. The new source is shown to be a reliable and attractive alternative for the growth of these phosphide materials.

Solid source molecular beam epitaxy of GaInAsP/InP: Growth mechanisms and machine operation

This article reports on the growth of GaInAsP/InP by solid source molecular beam epitaxy the incorporation efficiencies of the group V dimer and tetramer molecular species, and the functioning of the MBE system. The incorporation efficiency of As4 is found to be close to that of As2 while the incorporation efficiency of P4 is only half that of P2. Room temperature and low temperature photoluminescence measurements demonstrate that material grown using As4 is of better quality than that grown using As2. After the use of P4, a tenfold increase in the pressure burst occurs upon warming of the liquid nitrogen shrouds, and is believed to be caused by the formation of deposits containing white phosphorus. The atomic As to P incorporation ratio is approximately 10, when using P2, and exhibits a substrate temperature dependence.

InAs-based bipolar transistors grown by molecular beam epitaxy

Large mobilities and electron saturation velocity make InAs a promising material for high speed devices. Investigations into materials characteristics of doped InAs show nonideal behavior with standard molecular beam epitaxy dopants, silicon, and beryllium. Critical thicknesses for cracking of AlxIn1−xAs on InAs were empirically determined as a function of x. Mesa pn junctions in InAs show no effects of surface Fermi level pinning and exhibit good rectification with low reverse leakage. Bipolar junction transistor and heterojunction bipolar transistor devices are presented, along with their dc electrical characteristics. Common emitter current gains of 100 have been achieved in these bipolar devices.

BERYLLIUM DIFFUSION IN GAAS/ALGAAS SINGLE QUANTUM WELL SEPARATE CONFINEMENT HETEROSTRUCTURE LASER ACTIVE REGIONS

Beryllium (Be) diffusion into the active layers of single quantum well separate confinement heterostructure lasers grown by molecular beam epitaxy is investigated using photoluminescence absorption spectroscopy, secondary ion mass spectroscopy, capacitance–voltage profiling, and laser threshold current measurements. A significant amount of Be diffusion occurs under normal growth conditions. Large concentrations of Be in the quantum well are correlated to the lack of an exciton feature in the absorption spectrum. The amount of Be in the active region is reduced through a combination of lower Be concentration and lower growth temperature in the upper cladding region of the laser.

OPERATION OF A MOLECULAR-BEAM EPITAXY MACHINE EMPLOYING A VALVED SOLID PHOSPHORUS SOURCE

The use of an elemental source molecular‐beam epitaxy (MBE) machine for the growth of phosphides requires hardware and operating procedures different from those normally encountered in the growth of arsenides. The main hardware alterations are the use of valved group V cracker sources and different pumping schemes. Operating procedures must be developed to cope with higher operating pressures and flammable deposits. High‐quality phosphides and abrupt arsenide/phosphide interfaces are now possible using elemental source MBE.

Studies of ammonia dissociation during the gas source molecular-beam epitaxial growth of III nitrides

This article presents a method for the observation of ammonia dissociation during the gas source molecular-beam epitaxial (MBE) growth of group III nitrides. The mass spectrometer, present in most molecular beam epitaxy machines, is used to detect H2, a biproduct of ammonia dissociation. A direct line of sight, from the mass spectrometer to the substrate, is not required. The technique is used to examine several aspects of the MBE growth of AlN, GaN, and GaInN. Aluminum is approximately six times more efficient in causing ammonia dissociation than is gallium, which in turn is similarly more efficient than indium. During the growth of GaInN, transient effects in ammonia dissociation are observed following indium shutter actuations, indicative of indium surface accumulation.