Edge Facets Research Articles

Growth of Low Etch Pit Density (EPD) InP Crystals

Two-inch and 3-inch diameter S-doped dislocation-free (DF) (Dislocation density < 500/cm2) InP crystals were grown by the differently modified liquid-encapsulated Czochralski (LEC) method. Two-inch-diameter InP crystals were grown by the double thermal baffle method (DTB) and 3-inch-diameter crystals were grown by the phosphorus vapor controlled LEC method (PC-LEC). The DF S-doped InP crystals become somewhat rectangular in shape and the faceting on the body of the ingots takes place during the growth. The length of the edge facets in DF crystals is much longer than that of the Sn-doped InP crystals of which EPD is relatively high. We think that the difference in facet length can be explained by the difference in supercooling. To grow the DF single crystals, it is necessary to use the stoichiometric polycrystals without certain specific impurities.

Growth of Nd xGd 1− xCa 4O(BO 3) 3 along phase-matching direction and passive mode-locking self-frequency-doubling characteristics

Nd x Gd 1− x Ca 4O(BO 3) 3 (NdGdCOB) grown along the optimum phase-matching (PM) direction ( θ=66.8°, Φ=132.6°) is reported for the first time in this paper. The utilization ratio of the as-grown crystals along the optimum PM direction is improved up to 95% when the optical devices were processed, while it is only 50% for the crystals grown along 〈0 1 0〉 direction. It often shows two large (1 5 0) facets and growth edge facets on the as-grown crystal surface. The small facets on the shoulders were determined as ( 2 ̄ 0 1 ) facets by X-rays. The ( 2 ̄ 0 1 ) edge facets will vanish and ( 0 1 0 ) edge facets will emerge when the crystal is tapered. The (0 1 0) edge facets which anchor at the three-phase-boundary (TPB) are the principal cause for the formation of (0 1 0) twins. Passive modulated Q-switched and mode-locking green laser operation at 530 nm were achieved in NdGdCOB crystal using a xenon flash lamp as the pump source, Cr 4+ : YAG crystal as the saturable absorber with a plane-concave cavity, which is also reported here for the first time.

The influence of polarity on twinning in zincblende structure crystals: new insights from a study of magnetic liquid encapsulated, Czochralski grown InP single crystals

The polarity of {1 1 1} edge facets, anchored to the three-phase boundary (TPB), which give rise to growth-twin nucleation in the shoulder region of a [0 0 1], S-doped, magnetic liquid encapsulated Czochralski (MLEC) grown, InP boule, has been studied by chemical etching and synchrotron X-ray anomalous scattering. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on { 1 ̄ 1 ̄ 1 ̄ } P faces. Of the four possible sets of edge facets, belonging to the { 1 ̄ 1 ̄ 1 ̄ } P form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two of them can give rise to the conversion of a {1 1 5} external shoulder facet to a { 1 ̄ 1 ̄ 1 ̄ } P one upon twinning, while the other two can give rise to the conversion of a {1 1 4} external shoulder facet to a {1 1 0} one. In both cases, twinning is only observed when the { 1 ̄ 1 ̄ 1 ̄ } P edge facets are anchored to the TPB, in a region where the shoulder angle is close to 74.21 or 70.53°, facilitating the production of the {1 1 5} and {1 1 4} external shoulder facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.

The mechanism of growth-twin formation in zincblende crystals: new insights from a study of magnetic liquid encapsulated Czochralski-grown InP single crystals

Synchrotron white beam X-ray topography (SWBXT) [1, 2][M. Dudley, in: Mater Res. Soc. Symp. Proc., vol. 307, 1993, p. 213; Encyclopedia of Applied Physics, vol. 21, 1997, p. 533] combined with chemical etching and Nomarski optical microscopy have been employed to investigate the phenomenon of twinning in sulfur-doped, MLEC-grown 〈1 0 0〉 InP single crystals. Results confirm the prediction of Hurle [3, 4][Sir Charles Frank, OBE, FRS; on 80th Birthday tribute, 1991, p. 188; J. Crystal Growth 147 (1995) 239] that twins nucleate in regions where {1 1 1} edge facets are anchored to the three-phase boundary (TPB), and that twinning produces a {1 1 1} external facet on the shoulder region of crystal. The critical factor controlling the point at which the twin nucleates is observed to be the appearance of a {1 1 5} external shoulder facet which is then converted to the {1 1 1} external shoulder facet upon twinning. Based on the observation of both anchored edge facets and twinning at shoulder angles of approximately 74°, ν max, the maximum in the range of angles, ν (where ν is the angle between the edge facet and the extension of the crystal surface, or shoulder), over which edge facets can be expected to be trapped at the TPB, as presented by Hurle, has been increased, from ∼86.5° to ∼112°, by modifying approximations made concerning the relevant physical parameters for the particular case of S-doped InP. A correction is made to an error in Hurle: the most dangerous grow-out angle for the occurrence of twinning in 〈1 0 0〉 oriented crystals, is 74.2° and not 35.5°. Also Hurle predicted that, in crystals with diamond cubic or zincblende structures, the range of ν angles for edge facet pinning should encompass 70.5(3)° for twinning to be possible. This is here extended to the statement that it should encompass either 70.5(3)° and/or 109.47°. Incidences of twinning were also observed to occur by a similar mechanism but one which involved the conversion of a {1 1 4} external shoulder facet to a {1 1 0} one.

Influence of the crucible shape on the formation of facets and twins in the growth of GaAs by the vertical gradient freeze technique

The influence of the shape of the crucible on the growth of silicon-doped GaAs crystals by the vertical gradient freeze (VGF) technique is investigated by using four different angles Φ (60°, 90°, 120°, 144°) of the conical part of the pBN crucible. We find a decrease of the length of the {1 1 1} edge facets in the conical region with increasing cone angle Φ. The {1 1 1}As facets are always larger and show a higher tendency to twinning compared to {1 1 1}Ga facets. The model of Hurle (J. Crystal Growth 147 (1995) 239) which correlates the formation of twins with the growth of facets at the three phase boundary (TPB) is confirmed. The maximum angle between the edge facet and the extension of the crystal surface at which the facet should detach from the TPB is found experimentally to be between 95.3° and 107.3°, which corresponds well with the value of 104° calculated by Hurle for encapsulated GaAs.

The Mechanism of Twinning in Zincblende Structure Crystals: New Insights on Polarity Effects From a Study of Magnetic Liquid Encapsulated Czochralski Grown Inp Single Crystals

ABSTRACTSynchrotron White Beam X-ray Topography (SWBXT) and synchrotron X-ray anomalous scattering have been employed to determine the polarity of {111} edge facets, anchored to the three phase boundary (TPB) on which twinning is observed to nucleate in Magnetic Liquid Encapsulated Czochralski (MLEC) grown sulfur doped, &lt;001&gt; InP single crystals. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on {111}P faces. Of the four possible sets of edge facets, belonging to the {111}P form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two can give rise to a {115} to {111}P external shoulder facet conversion upon twinning, while the other two can give rise to a {114} to {110} conversion. For these cases, twinning is only observed when the {111}P edge facets are anchored to the TPB in a region where the shoulder angle is close to 74.21° or 70.53°, facilitating the production of the {115} and {114} external shoulder facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.

A mechanism for twin formation during Czochralski and encapsulated vertical Bridgman growth of III–V compound semiconductors

Conditions are derived for which nucleation in twin orientation on an “edge” facet during the Czochralski growth of semiconductors is thermodynamically favoured over nucleation in the correct orientation. The model is based on ideas presented by Voronkov [Sov. Phys.-Cryst. 19 (1975) 573] concerning the conditions necessary for the edge facets to be anchored at the three phase boundary. It is shown that the conditions are satisfied for GaAs, InP and InSb but not for Ge and Si. The main features of twinning in the III–V compounds are accounted for and predicted conditions for the avoidance of twinning are listed.

The Structure of Thin Gold Films at the Early Stage of Continuous Film Growth

The use of a transmission electron microscope to observe surface structure of thin films has been demonstrated in recent years by diffraction contrast imaging to ∼ 10Å resolution using the forbidden reflections of [111] Au and at atomic resolution using bright-field phase contrast on both [001] and [111] oriented Au films. It has also been possible to demonstrate that beyond a minimum thickness, these films can be free standing and viewed in the microscope without significant modification due to the incident electron beam generating sputtering events at high beam currents. It is therefore now possible to obtain free standing [001] Au films which exhibit various types of surface topography. These films were obtained by varying the growth parameters with a microprocessor controller attached to a UHV deposition system. The deposition of Au was precisely controlled onto a thick Ag substrate which was initially deposited upon NaCl single crystals.Fig. 1 shows a low magnification image ∼ 40Å thick [001] Au film grown at a vacuum level of 5 × 10-9 Torr, 50° substrate temperature and a deposition rate of ∼ 1/20 ML/sec. Clearly defined atomic step regions are visible as demonstrated by the terrace-like contrast variations over extended regions i.e. a step-ledge growth regime. Regions between these terrace areas represent coalescence of individual grains which were not attached at an earlier stage of growth. These regions exhibit finer scale terraces and ledges which follow either &lt;100&gt; or &lt;110&gt; directions as evidenced by comparing their directions to stacking faults and twins occasionally observed in the field of view. Small holes are also present which have crystallographic edge facets and anomalous contrast bands also occur which represent the lack of tracking of the upper surface layer growth to steps which exist at the lower surface. Fig. 1 was obtained by diffraction contrast from the direct beam alone. It was not necessary to use the forbidden reflections here since they produced too drastic a contrast change.

Characterization of growth cells in In-doped GaP crystals by birefringent method

Growth cells in 1.7 at% In-doped liquid encapsulated Czochralski GaP crystals grown with different rotation conditions have been characterized by both macroscopic and microscopic birefringent methods. The initiation positions and the size of growth cells in crystals were found to be dependent on the rotation conditions during crystal growth. In crystals grown under counter-rotation conditions, the growth cells were large enough to be visually observed and were observed to be easily initiated from both the edge tips on the facet/nonfacet interface and the surface of the crystal shoulder. In the shoulder region, the growth cells were found to be usually accompanied by solute trails, and they disappeared when the crystal diameter became large. In the crystal grown under crucible-dominated co-rotation conditions, the growth cells are so small that they can only be observed under a microscope. In the crystal grown under crystal-dominated co-rotation conditions, only edge facets were observed.