Re: How could you make ZnS into an n-type and p-type conductors

Dear Linda Quest:
To my knowledge ZnS is not used as a semiconductor in the sense that it can 
be doped to make n or p type conductivity.  However, by doping ZnS crystals 
with small amount of impurity (~0.5% copper or silver) it becomes a 
phosphor which means that when it is struck by ultraviolet light, nuclear 
particles, or energetic electrons it emits light.  This is a solid-state 
pehnomena similar to doping of other semiconductors; the way this is done 
is to mix the zinc sulfide with ~2% sodium chloride plus the metal impurity 
being added, and fired in a non-oxidizing atmosphere to avoid oxidation of 
the zinc.  In this process the materials melt together and then reform 
modified doped crystals at 1020 degrees C.  These are phosphorescent, and 
can be mixed with a binder and spread on a surface like a paste and baked. 
 The result is a phosphorescent surface which emits light for a small 
period of time after the exposure to an energy source like an electron 
beam. This is how a cathode-ray tube works, and many kinds of optical 
displays use ZnS films of this type.

ZnS is also electroluminescent, which means that if you put the crystals 
between two electrodes and apply a voltage conduction electrons in the 
crystal gain enough energy to excite atoms during collisions and cause them 
to give off visible light.  This is similar to the situation in a 
semiconductor device except that light is emitted.  Although ZnS is a 
semiconductor, it's electrical conductance is too low to make it suitable 
for making devices like transistors where electric currents are employed.  
Instead it finds it's  semiconductor use as light source for viewing 
screens, etc.

ZnS crystals are very small; you cannot grow ingots of single-crystal ZnS 
like you can of Silicon.

I hope this reply is helpful to your student.

Sincerely, Dick Bersin........