Large-diameter Substrates Research Articles

Cost-effective, high-volume molecular beam epitaxy using a multi 6-in wafer reactor

The rapidly expanding market of wireless communication has drastically increased the demand for GaAs-based devices and circuits. This demand has driven the industry to increasingly larger diameter substrates for cost-effective, high-volume production. IQE Inc., a division of IQE plc has recently developed the technology to grow epitaxial structures on 150 mm (6-in) GaAs substrates using a multi 6-in wafer MBE platform with material characteristics exceeding those achieved on a multi 4-in platform. The new platform is configured to produce four 6-in epiwafers per platen and is projected to produce up to 21 000 wafers per year. This paper presents the methodology that was chosen to qualify the reactor for production. Discussions focus on machine performance, material quality, and capability. In-depth discussions of capacity, throughput, and reproducibility are included. The advantages of using statistical process control for high-volume production are presented.

Uniformity and Performance Characterization of GaN p-i-n Photodetectors Fabricated from 3-Inch Epitaxy

Gallium nitride wafer epitaxy on large diameter substrates is critical for the future fabrication of large area UV linear or 2D imaging arrays, as well as for the economical production of other GaN-based devices. Typical group III-nitride deposition is now performed on 2-inch diameter or smaller sapphire substrates. Reported here are visible blind, UV GaN p-i-n photodetectors which have been fabricated on 3-inch diameter (0001) sapphire substrates by RF atomic nitrogen plasma MBE. The uniformity across the wafer of spectral responsivity and shunt resistance (R0) for the p-i-n photodetectors has been characterized. Spectral responsivity and 1/f noise as a function of temperature exceeding 250°C will be presented for the GaN p-i-n photodetectors. Spectral response with >0.17 A/W at peak wavelength and having 4-6 orders of magnitude visible rejection has been achieved. 1/f noise typically less than 10−14 A/Hz1/2 at room temperature also has been achieved with GaN p-i-n photodiodes. The results have been correlated with proposed models for dark current and 1/f noise in GaN diodes.

Functional and adaptive significance of primate pads and claws: evidence from New World anthropoids.

This study tests predicted morphoclines in fingertip morphology among four small-bodied (<1 kg) New World monkeys (Saimiri sciureus, Leontopithecus rosalia, Callithrix jacchus, and Saguinus oedipus) in order to test previous functional and adaptive explanations for the evolution of flattened nails, expanded apical pads, and grasping extremities within the Order Primates. Small-bodied platyrrhines which frequently forage among small-diameter substrates are expected to possess 1) relatively expanded apical pads, 2) well-developed epidermal ridges, 3) distally broad terminal phalanges, and 4) reduced flexor and extensor tubercles compared to those species which use large-diameter arboreal supports more frequently for their locomotor and postural behaviors. Results show that as the frequency of small-branch foraging increases among taxa within this sample, relative distal phalanx breadth also increases but distal phalanx length, height, and flexor tubercle size decrease. Moreover, epidermal ridge development becomes more pronounced as the frequency of small-branch foraging increases. Terminal phalanx breadth and epidermal ridge complexity are both positively correlated with apical pad size. The large, flexible apical pad increases stability of the hand and foot on small-diameter arboreal supports because the pad can contact the substrate in several planes which, in turn, enables the pad to resist disruptive forces from different directions by friction and interlocking (Hildebrand, 1995). The observed morphoclines demonstrate that a gradient in form from claw- to nail-like tegulae exists among these taxa. Thus, the distinction between claw- and nail-bearing platyrrhines is essentially arbitrary. These observations corroborate Cartmill's (1972) functional and adaptive model for the loss of claws in primates: namely, expanded apical pads are required for habitual locomotor and postural behaviors on small-diameter supports whereas claws are more useful for positional behaviors on large-diameter substrates. Finally, results from this study support previous suggestions that the keeled tegulae of callitrichines represent a derived postural adaptation rather than a primitive retention from an ancestral eutherian condition.

Functional and adaptive significance of primate pads and claws: Evidence from New World anthropoids

This study tests predicted morphoclines in fingertip morphology among four small-bodied (<1 kg) New World monkeys (Saimiri sciureus, Leontopithecus rosalia, Callithrix jacchus, and Saguinus oedipus) in order to test previous functional and adaptive explanations for the evolution of flattened nails, expanded apical pads, and grasping extremities within the Order Primates. Small-bodied platyrrhines which frequently forage among small-diameter substrates are expected to possess 1) relatively expanded apical pads, 2) well-developed epidermal ridges, 3) distally broad terminal phalanges, and 4) reduced flexor and extensor tubercles compared to those species which use large-diameter arboreal supports more frequently for their locomotor and postural behaviors. Results show that as the frequency of small-branch foraging increases among taxa within this sample, relative distal phalanx breadth also increases but distal phalanx length, height, and flexor tubercle size decrease. Moreover, epidermal ridge development becomes more pronounced as the frequency of small-branch foraging increases. Terminal phalanx breadth and epidermal ridge complexity are both positively correlated with apical pad size. The large, flexible apical pad increases stability of the hand and foot on small-diameter arboreal supports because the pad can contact the substrate in several planes which, in turn, enables the pad to resist disruptive forces from different directions by friction and interlocking (Hildebrand, 1995). The observed morphoclines demonstrate that a gradient in form from claw- to nail-like tegulae exists among these taxa. Thus, the distinction between claw- and nail-bearing platyrrhines is essentially arbitrary. These observations corroborate Cartmill's (1972) functional and adaptive model for the loss of claws in primates: namely, expanded apical pads are required for habitual locomotor and postural behaviors on small-diameter supports whereas claws are more useful for positional behaviors on large-diameter substrates. Finally, results from this study support previous suggestions that the keeled tegulae of callitrichines represent a derived postural adaptation rather than a primitive retention from an ancestral eutherian condition. Am J Phys Anthropol 106:113–127, 1998. © 1998 Wiley-Liss, Inc.

Uniformity and Performance Characterization of GaN P-I-N Photodetectors Fabricated From 3-Inch Epitaxy

AbstractGallium nitride wafer epitaxy on large diameter substrates is critical for the future fabrication of large area UV linear or 2D imaging arrays, as well as for the economical production of other GaN-based devices. Typical group III-nitride deposition is now performed on 2-inch diameter or smaller sapphire substrates. Reported here are visible blind, UV GaN p-in photodetectors which have been fabricated on 3-inch diameter (0001) sapphire substrates by RF atomic nitrogen plasma MBE. The uniformity across the wafer of spectral responsivity and shunt resistance (R0) for the p-i-n photodetectors has been characterized. Spectral responsivity and 1/f noise as a function of temperature exceeding 250°C will be presented for the GaN p-i-n photodetectors. Spectral response with &gt;0.17 A/W at peak wavelength and having 4-6 orders of magnitude visible rejection has been achieved. 1/f noise typically less than 10-14 A/Hz1/2 at room temperature also has been achieved with GaN p-i-n photodiodes. The results have been correlated with proposed models for dark current and 1/f noise in GaN diodes.

Low dislocation density Si-doped GaAs single crystal grown by the vapor-pressure-controlled Czochralski method

Si-doped GaAs substrates have been widely used for optical devices. Recently, as the device fabrication process has changed, larger diameter substrates can be used. Almost dislocation-free Si-doped GaAs crystals of 75 mm diameter, which are suitable for the fabrication of optical devices, have been successfully grown using our vapor-pressure-controlled Czochralski (VCZ) method. The generation of slip dislocations could be suppressed and the growth of the dislocation-free crystal was achieved by decreasing the thickness of B2O3. The VCZ crystals contained a large amount of unintentionally doped boron (B) of about 1018 cm−3. By comparing the electrical data of the VCZ crystals with those of the gradient freeze (GF) crystal free from B, it is found that B acceptors decrease the intrinsic compensation ratio ([SiAs][SiGa]).