Interesting , got a package, ...233 model:
diode has very high internal impedance, this lead it to very sensitive to a current flow. I'm still puzzle about why 2 diodes in a package, noy a single, or let say 4, or 6 .... and common cathode, seems, due-to manufact. process. Anyway:
2 internal diodes in parallel, just to decrease the diode internal resistance, hook to a precision voltage source, + 2 variable multi-turn resistors, 10K + 100, 100 ohm - give an option to dial up a fraction of microamp. So heating, cooling, adjusting current, I received 2-3 ppm/C in a range 20-30C. Thinking , of 6-8 in parallel, with 50 ohm multi-turn trimpot to adjust current for optimal temp stability, and possible to dial each to diff rising or falling temp. trend, it may allow me to compensate temp. further
With total 3.7 ma current, it observe a self heating.
while I waiting trimpots ( takes weeks, i think) will do an aging\torching process ... will see ...