Sb on Si(111)
Notes:
This is in very early stages, and needs further optimization
Day before:
HF dip and load sample.
Growth day:
Morning: heat up Al or Ga (to getter Sb)
Go to lab
Put Sb sublimator in manual, power output to 72
Move trolley from LC to BC. Close gate valve. Load first Si wafer onto HTS. Move trolley as far as possible from HTS. Bake for 1 hour at 450 C.
Set HVP to 25
Record background pressures
Make sure CAR is in transfer position
Run Sb coarse STO - because the Sb sublimator is optimized for III-V growth with a much higher Sb BEP, the small Sb BEP needed is right around the edge where the valve starts to open. The open position varies quite a bit between individual growth days. The purpose of the coarse STO is to determine where the Sb valve opens.
Run Sb fine STO - optional, can do if you want to be very specific about the growth rate.
Note - Sb STO recipes open Sb valve to 140, then to desired position. Failing to do this can prevent the Sb valve from opening fully. According to Siff and Rodolfo, the Sb valve experiences hysteresis, so it's important to distinguish between BEPs measured when the valve is closing vs opening. Because we are opening to a higher valve position first, the BEP will always be measured when the valve is closing.
Double check the BEP manually
Turn off beam flux IG
Idle the Group III cell
Ramp up RHEED to 1.5 A and 10 kV
After HTS bake, set HTS to 10, wait for temperature to drop below 250 C
Move first sample from HTS to GC
Move first sample from HTS to trolley
Set substrate heater to manual
Open GV between GC and BC, then shutter. Make sure to lock shutter in open position
Transfer off RHEED block
Transfer in first sample
Close shutter, then GV
Put substrate heater back in auto, set to 450 C for away bake (10 - 15 minutes)
Transfer second sample to HTS, start second sample HTS bake
After away bake, start "deox" bake (not a true deox, actually desorbing hydrogen passivation + any crap)
Rotate CAR to growth position
Open RHEED to check wafer has made it
Start substrate rotation
Set substrate temperature to 750 C (thermocouple)
Stop substrate rotation (rotating above 800 C may damage the CAR bearings)
Set substrate temperature to 990 C (thermocouple)
Deox bake for 15 minutes at 990 C thermocouple. This should be 740-760 C pyro. Since it's the max temperature, and I use it every time, I don't check with the pyro on every growth. The pyro doesn't monitor the low temperatures I need for growth very well, and black body doesn't work well for Si, so I use the thermocouple (TC) for everything.
After deox, cool down and face cryoshroud
Note: Sb needs to be grown much hotter than Bi or BiSb, because of it's lower adatom mobility. Antimonene/Ge paper puts the ideal temp around 270 C. There's a difficult balance here between desorbing too much Sb and growing the Sb too cold, which is made more difficult by the poor temperature calibration of the pyro at this temperature. Seth suggests measuring the pyro temp at each TC temp in steps between 800 C and whatever point the pyro stops working, and then extrapolating the pyro temperature at the TC you use for growth. I haven't done this yet.
Set substrate temp to 5 degrees below desired growth temp
When TC < 750 C, start substrate rotation
Wait in MBE lab for substrate to cool down. It's much shorter.
When TC is about 10 degrees above growth temperature, set substrate heater to manual, and try to control manually to avoid overshooting
Monitor with pyro as well as possible - try to get around 270
When you're happy with the substrate temperature, manually set Sb valve to 140 with shutter closed (to avoid blasting wafer with Sb early in growth)
Set Sb valve to calibrated value with shutter closed
Run Sb growth recipe
Monitor with RHEED and record and double line / 1x1 transition. TBD which structures are forming.
After growth, promptly transfer first sample to trolley
Replace with second sample and repeat as applicable
After finishing all growths
Transfer RHEED block back in
Move trolley with grown wafers to LC
Ramp down RHEED
Set Sb sublimater to auto at same temperature as it is at the end of growth
Turn on BF gauge
Set HTS to normal temp
Any other standard procedures I forgot to list
Unload sample and load for next grower
Note - Sb probably oxidizes much faster than Bi, limit air exposure