Cornell GSMBE
The INTEVAC modular GEN-II gas source molecular beam epitaxy (GSMBE) machine in the Cornell MBE Facility was installed in 1995. It is presently used for the growth of III-nitride (GaN) compound semiconductors.
Early experience was with the Oxford Research Cars-25 remote RF plasma source of atomic nitrogen. The optical atomic nitrogen signal as a function of background pressure shows that greatest efficiency occurs at lowest pressures, while the highest total amount of atomic nitrogen is obtained at highest pressures.
A Kaufman ion source was also installed and saw limited use. The source has only lasted for 3 growths. So far, the results are remarkable. These are the only GaN growths we have performed that exhibit no room temperature photoluminescence.
A new atomic nitrogen source was installed on May 23, 1997. The unibulb atomic nitrogen source from EPI replaces the Kaufman source and is being compared to the Oxford source. Growth rates beyond 0.6 microns/hr have been routinely obtained. Some early mobilities beyond 200 cm2/vsec at 300K for 1E18 n-type material were obtained
The RF source underwent a repair during the Fall of 1997. Since that time, several changes have been made to the operating environment and source degredation is absent over a period of more than 1 year. Growth rates of 0.9 to 1.0 µm/hr are routinely employed. A few wafers grown at 1.4µm/hr look quite good. These growths were made at 350W. More details of MBE GaN are found in the MURI reports.
The 8 sources are:
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Be |
Be from Varian thermal furnace |
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RGA |
Stanford Research Systems residual gas analyzer |
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Mg from Varian thermal furnace |
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Ga |
Ga from EPI thermal furnace |
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Al from Varian thermal furnace |
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In |
In from Varian thermal furnace |
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Si |
Si from Varian thermal furnace |
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N |
Atomic N - EPI Unibulb RF Source |
The SRS RGA was installed in a furnace port in July 1997 to observe Ga desorption from GaN surfaces. Data will be posted when it becomes available. This quad is a very solid instrument. We highly recommend it for MBE applications.
Some pictures from inside the machine are available. They were taken on March 19, 1998 looking through the turbo port. They range in size from 150Kb to 300Kb.
Looking at the turbo gate valve1
The GSMBE in a state of re-assembly
Maintenance Logs
August 2001 - Water leak into nitrogen purge line
September 2001 Vacuum pump for LN2 system
October 2001January 2002 - roughing cart
LN2 system log
Last modified: 11-Jan-2002 13:03:17 .
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