🚀 go-pugleaf

    Hellow, I am a student in Japan.   And I use ANELVA S830 MBE
system.

>   Some one must have done this - low substrate temperature measurment for MBE.
>
>   We have a much modified (and now very old) Varian 360 MBE which we use for
>   growth of InGaAs/GaAs layers (MQWs for modulators and 980 nm lasers).
>   Currently we measure the substrate temperature in two ways -

I think you grow InGaAs/GaAs at Tsub=450 degree C or so.

>   1) We have a thermocouple attached to a sapphire bead which is supposed
>   to be in contact with the back of the Mo block (we still indium solder
>   our wafers but put silicon nitride or dioxide on the back which overcomes
>   a lot of the problems).  In practice, the sapphire bead doesn't touch the
>   back and we rely on radiative coupling to the bead (which isn't too bad at
>   high temps).

Thermocouples at substrate heater do not touch enough also in our
system.    I do not believe the temperature of the thermocouple.
It changes from +100 to -100 degree C while a substrate is rotated.

>   The system is calibrated using the Al/Si eutectic temperature.  We have
>   looked at using the oxide desorption temperature but seem to have a problem
>   with our substrate cleaning so that the desorption temperature appears
>   to vary by about 50 C from run to run.  (Anyone willing to tell me 
>   EXACTLY what their favourite cleaning recipe is?? - I've seen lots of
>   very brief descriptions but no real details.  We currently use a sulphuric
>   acid / hydrogen peroxide etch.)

I think the reason of the errors of your pyrometer cannot be put
the blame on your pyrometer.     The temperature showed by
pyrometer dependes on solid angle to the substrates so that the angle
of the substarates are not constant in each run.

>   Anyway, the problem (at last) is that we need to measure lowish temperatures
>   now (of the order of 300-500 C) and we would like some recommendations of how

In our laboratory, Tsub is calibrated by Al/Si for high
temperature (for GaAs and AlAs growth) and Au/Si for low
temperature (for InAs growth).  And I get the relation between the
Tsub and the heater current.  The lineality of the heater current
and Tsub is also checked with pyrometer in the region between 
the eutectic temepratures of Al/Si and Au/Si .

In practice, windows get more and more dirty with As(GaAs?) in
every runs.    I think pyrometer cannot bring true results in any
time.    What I believe is the heater current and RHEED pattern.

If you want to get more detail about our fasion, please send
e-mail to me.   ( But I cannot say 'leave it to me!'. )

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                    e-mail : uno@kuee.kyoto-u.ac.jp