Quaternary alloys can be created by using a ternary alloy and a compound semiconductor as base materials. The ternary alloy (which itself is created by mixing two compound semiconductors) is an 'alloy' type material and it should be converted to 'semiconductor' type before it can be used as a base material for the quaternary alloy. The compound semiconductor will in most cases be available in the material database. As an example, steps to creating AlxGayIn1-x-ySb in CHARGE is shown below:
The AlxGayIn1-x-ySb quarternary alloy can be created by mixing AlSb, GaSb, and InSb. The first step would be to mix InSb and AlSb together to create In1-xAlxSb. Next, the alloy is converted into a semiconductor type material, and then finally, the semiconductor model of In1-xAlxSb is mixed with GaSb to get AlxGayIn1-x-ySb.
Step 1: Create alloy model for In1-xAlxSb
Create a new alloy using the 'Ternary Alloy' option under the 'new material' button. Choose InSb as the first base material and AlSb as the second base material. Choose the interpolation option to be 'multi valley'.
Set the name to be In(1-x)Al(x)Sb. Since InSb is the first and AlSb is the second base material, the alloy mole fraction will be (InSb)1-x(AlSb)x or In1-xAlxSb.
NOTE: The default electrical material database in CHARGE comes populated with the common ternary alloys. If the database already contains the desired ternary alloy then it is recommended to use the existing model rather than creating one from scratch.
Step 2: Convert In1-xAlxSb to semiconductor type material
Use the "Convert to semiconductor" option available in the duplicate menu to convert the created alloy into a semiconductor type of material:
This enables InAlSb to be used as a base material in the next step. The option will prompt the user to set the mole fraction x, here corresponding to AlSb.
It should be noted that the values obtained for the new semiconductor are approximations, and the created material may still require user inspection. The minimum semiconductor material properties that are necessary to create the 'semiconductor' material model of In1-xAlxSb are permittivity (epsr), work function (W), bandgap (Eg), electron and hole effective mass (mn, mp), electron and hole mobility (mun, mup), and the carrier lifetimes for SRH recombination (taun, taup).
Step 3: Create the quaternary alloy AlxGayIn1-x-ySb
Finally, use the new semiconductor material model for In1-xAlxSb (In(0.55)Al(0.45)Sb) and GaSb to create a 'Ternary Alloy' material model for AlxGayIn1-x-ySb. Name the material Al(0.45)Ga(y)In(1-0.45-y)Sb.
Note: The actual alloy mole fraction for the new alloy should be In(1-x)(1-y)Alx(1-y)GaySb. However, for the case where x and y are both small enough so xy << x or y, we can rewrite the alloy mole fractions as AlxGayIn1-x-ySb.