GaAs RHEED Oscillations

Written from NTS notes NTS, 5/6/2015

Note: Must have sample loaded and in the GC growth position ready to grow (already De-oxed, or as part of your recipe).

Note: RHEED gun must be ramped up and ready. EZ RHEED software and BandiT software (or other temperature method) must be open.

Prep and Start Growth

1. Write your recipe for this growth

   1. It might just be a buffer layer and you do everything else by hand in Amber

   2. You might automate everything and just have a waitop step for doing RHEED

   3. Or somewhere in between, etc.

2. Double check your recipe for proper shuttering and Group V valve control

   1. You want the As shutter to be open the entire time

      1. The needle valve should be open the entire time too (value > 100)

      2. E.g. Place an open As command before you start your first buffer layer, or the As shutter might close after the GaAs layer, and you won’t be able to open it remotely during a waitop

3. Also note you can’t remotely shutter Ga during a waitop, but using the shutter box is fine. Remember to put Ga back in remote after!

4. Start your recipe, which likely physically starts with a buffer layer of 500-2000 A GaAs (or a Deox, but I’m assuming that is done)

5. When the buffer layer is done, depending on how your recipe is written, something will happen to tell you it’s time for RHEED oscillations

6. Make sure there’s still an As overpressure, and know how you will shutter the Ga

7. Note: RHEED Oscillations always have a Group V overpressure, As for GaAs.

8. Lower the sample BandiT temperature to the proper temperature for RHEED Oscillations

9. 530 C is standard for 2x4 reconstruction GaAs, which is standard

10. 2x4 perpendicular; 4x4 on diagonals: C4x4

    1. Going under 500 C can lead to 4x4 reconstruction GaAs, which you might want

       1. 4x4 perpendicular; and 2x2 on diagonals: C2x2

11. Close Ga shutter

12. Stop substrate rotation

13. Put CAR into manual

14. Rotate by hand to the 2x reconstruction or brightest spot

15. The 2x should look bright and ~symmetric on top and bottom of the specular spot

16. Check that it’s a true 2x by comparing to the 4x first order fringe with a RHEED software on-screen box

RHEED Software

1. Zoom in on specular spot (Zeroth order fringe)

2. Select a box, one pixel wide and much taller, somewhere in the specular spot

   1. Choose a spot and use it each time, e.g. left of center

   2. Or box, same height as the specular spot, covering the right side and the tail

3. Set gain to an appropriate value (~400-900) so the specular spot looks good

4. Set shutter to an appropriate value (~0.01 to 0.1) for same

   1. Shutter is software shutter, limited by mechanical shutter

   2. Used ~800-900 and ~0.05 on B150506A

5. On EZ RHEED software, open the Intensity Oscillations tool

6. EZ RHEED > Tools > Intensity Oscillations

7. Setup the software for oscillations

8. A/sec/osc: monolayer constant

   1. GaAs: a = 5.654 A; ML = 2.827 A

9. Check Enter oscillations manually

10. Check manual peak find

RHEED Oscillations

1. Click acquire time data to start recording

2. Open Ga

   1. Manually if using waitop or with Amber if other method, etc.

3. Get RHEED Osc

4. We want 8 to 15 max, or 6/7 if it degrades a lot

5. Click Stop time data

6. Close Ga

7. Align cursors with peaks

   1. Skip all of first true peak

8. Count and enter peaks

9. Click calculate

10. Repeat as desired, growing GaAs normally in between to smooth out surface

11. Note: We want the initial RHEED Oscillation intensity to be ~100. If it’s lower, we can click Acquire time data (don’t open Ga), raise gain to set intensity, and click stop data. Then proceed as normal.

12. When you’re done, remember to set shutters in necessary configurations

13. Ga in remote

14. As in remote. Or you can flip it to remote right after resuming recipe if using waitop.

    1. It’s OK if you need to close As for a second (with needle valve open)