- Email: [email protected]
VG semicon: the vital component for MBE
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VG VG Semicon has always been at the leading edge of MBE technology; this reputation has been based on a highly successful range of systems. At the moment of launch for a new series of brochures, this New Products Feature takes a closer look at three new M BE components from VG Semicon. he performance of MBE systems can only be as good as the performance of the components from which they are built, and this area has received considerable attention. So says Mike Czerniak, VG Semicon's new Product Manager, "The resulting improvements in performance are truly significant in line with our philosophy of being Better by Design".
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Hot lip cell These are commonly used where the condensation of source material from a thermal effusion source is undesirable. Examples are gallium, which can form droplets that are related to the generation of oval defects in the epitaxial layer, and antimony, which can form a crust that lowers the effective beam flux and reduces its incorporation as a dopant.
500°C
In many applications, such as chemical beam epitaxy (CBE), or where As2 molecules are present, there is a tendency for viewports and R H E E D screens to become coated with deposits which can quickly reduce their
transparency. The use of conventional flap-type shutters cannot prevent this because the evaporant molecules are sufficiently mobile to find their way around the edges. At VG Semicon, this problem has been addressed by adding fixed shielding around the edge of the shutter flap, thereby requiring multiple collisions for a molecule to pass around the flap, effectively screenmg the viewport. This component, together with the full range of conventional shutters, is now operated by a magnetic linkage, eliminating bellows from the mechanism. The effect is to enhance reliability, minimise particulates and virtually eliminate the possibility of leaks. These magnets, whi'ch are external to the vacuum envelope, can be baked up to 250°C and are simply r e m o v e d for higher t e m p e r a t u r e bakeouts.
600°C
700°C
By paying careful attention to the thermal profile of the VG Semicon design, enhanced by innovative use of materials, an effusion cell has been produced that gives true hot lip performance over a surprisingly wide range of temperatures. This is illustrated by the sequence of unretouch.ed photographs. In all cases, a temperature differential of at least 60°C is m a i n t a i n e d between the crucible orifice and its body. Also evident is the excellent thermal uniformity of the latter for maximum beam stability.
Gas baffle shutters
Pa0e l lVo 6N°3
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Wobblesticks The advantages of magnetic coupling, as outlined above, have also applied to the new range of wobblestick sample transfer devices. A particular advantage over the original bellows coupled design is that, because linear movement is transmitted magnetically, atmospheric pressure does not influence the movement of this device. This allows much more accurate movement. -
Flexible range As Mike points out, "all the above components are featured in the appropriate VG Semicon systems, which range from the flexible V80H research machine to the V100 for full-scale production applications, and are also available as individual components". Gas Baffle Shutter.
VG Semicon has also been successful in sales of complete systems. USbased merchant epiwafer supplier, Quantum Epitaxial Designs, QED, has announced the purchase of a V100 multiwafer production MBE system. This will bring the total number of V100 systems in the field to five. Other systems news from VG Semicon is the successful installation and operation of a V80H GSMBE system to the recently opened Sharp Laboratories Europe research facility for optoelectronic materials research. Finally, a new series of literature is now available from VG Semicon, each featuring a different aspect of MBE, copies are available by writing to Miss Julia Harris at the address below. VG Semicon, The Birches Industrial Estate, Imberhorne Lane, East Grinstead, West Sussex RH19 1XZ UK. Tel~fax: [44] (0)342 324011 / 315800.
Magnetically-Coupled Wobble-Sticks.
Page 45
I
Vol 6 No 3
~....~:~
: : - ~ : .......................... .......................................
........
~.~
VG VG Semicon has always been at the leading edge of MBE technology; this reputation has been based on a highly successful range of systems. At the moment of launch for a new series of brochures, this New Products Feature takes a closer look at three new M BE components from VG Semicon. he performance of MBE systems can only be as good as the performance of the components from which they are built, and this area has received considerable attention. So says Mike Czerniak, VG Semicon's new Product Manager, "The resulting improvements in performance are truly significant in line with our philosophy of being Better by Design".
T
Hot lip cell These are commonly used where the condensation of source material from a thermal effusion source is undesirable. Examples are gallium, which can form droplets that are related to the generation of oval defects in the epitaxial layer, and antimony, which can form a crust that lowers the effective beam flux and reduces its incorporation as a dopant.
500°C
In many applications, such as chemical beam epitaxy (CBE), or where As2 molecules are present, there is a tendency for viewports and R H E E D screens to become coated with deposits which can quickly reduce their
transparency. The use of conventional flap-type shutters cannot prevent this because the evaporant molecules are sufficiently mobile to find their way around the edges. At VG Semicon, this problem has been addressed by adding fixed shielding around the edge of the shutter flap, thereby requiring multiple collisions for a molecule to pass around the flap, effectively screenmg the viewport. This component, together with the full range of conventional shutters, is now operated by a magnetic linkage, eliminating bellows from the mechanism. The effect is to enhance reliability, minimise particulates and virtually eliminate the possibility of leaks. These magnets, whi'ch are external to the vacuum envelope, can be baked up to 250°C and are simply r e m o v e d for higher t e m p e r a t u r e bakeouts.
600°C
700°C
By paying careful attention to the thermal profile of the VG Semicon design, enhanced by innovative use of materials, an effusion cell has been produced that gives true hot lip performance over a surprisingly wide range of temperatures. This is illustrated by the sequence of unretouch.ed photographs. In all cases, a temperature differential of at least 60°C is m a i n t a i n e d between the crucible orifice and its body. Also evident is the excellent thermal uniformity of the latter for maximum beam stability.
Gas baffle shutters
Pa0e l lVo 6N°3
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::::?~$......::~:~: ::~,8:.. :::::::::::::::::::::::::::::::::::::::::::::::: :~:-::~:~.::: :::::::::::::::::::::::::::::::::::-~::~: :::::
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.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Wobblesticks The advantages of magnetic coupling, as outlined above, have also applied to the new range of wobblestick sample transfer devices. A particular advantage over the original bellows coupled design is that, because linear movement is transmitted magnetically, atmospheric pressure does not influence the movement of this device. This allows much more accurate movement. -
Flexible range As Mike points out, "all the above components are featured in the appropriate VG Semicon systems, which range from the flexible V80H research machine to the V100 for full-scale production applications, and are also available as individual components". Gas Baffle Shutter.
VG Semicon has also been successful in sales of complete systems. USbased merchant epiwafer supplier, Quantum Epitaxial Designs, QED, has announced the purchase of a V100 multiwafer production MBE system. This will bring the total number of V100 systems in the field to five. Other systems news from VG Semicon is the successful installation and operation of a V80H GSMBE system to the recently opened Sharp Laboratories Europe research facility for optoelectronic materials research. Finally, a new series of literature is now available from VG Semicon, each featuring a different aspect of MBE, copies are available by writing to Miss Julia Harris at the address below. VG Semicon, The Birches Industrial Estate, Imberhorne Lane, East Grinstead, West Sussex RH19 1XZ UK. Tel~fax: [44] (0)342 324011 / 315800.
Magnetically-Coupled Wobble-Sticks.
Page 45
I
Vol 6 No 3