Vertical Vs. Lateral 

Undercut Vs. Oxidation 

Undercut vs. Oxidation:

undercut gives high Q, but low thermal insulation

an AlAs substrate can be oxidized to an index of ~ 1.5, which should still give high Q.


Electrical Pumping:

Ohmic contact: Hard to get with n side. Usually use Ge/Au (can be MBE grown). On p side can use a variety of materials Ti/Au. 

Lithography requirements:

can have two approaches vertically vs laterally doped structure. both should work. vertical may be easier and less costly, because the p-i-n junction is grown into the wafer, whereas the p-i-n has to be implanted or grown into the lateral structure.


Vertical Doping:

    contacts:
         p contact ohmic contact may not be necessary since a degenerately doped layer can be grown on top for contact
         n contact with in solder diffusion  or etch:
                    etch precision control.
    lithography:
         i) two steps + in contact (with degenerate doping - one step + in contact) ***
         ii) two steps + lithography
  

Lateral Doping:
    contacts:
        p ohmic contact done in one step then both p and n
        if there is high doping of p side, can do both contacts in one step.
   
    2 lithography steps max for contacts
    2 lithography steps for implantation or deposition mask

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