Compound Semiconductor Materials
For example, within a given target spectral resolution and detection efficiency, it is usually possible to select from a range of stopping powers. Choosing materials with the largest stopping powers enables thinner detectors to be produced with resulting benefits in radiation tolerance (which is a bulk effect) and lower leakage currents. By careful choice of both band gap and stopping power it is possible to fabricate detectors with a very wide dynamic range but sub-keV energy resolution in the soft X-ray band and tens of keV in the gamma-ray band. For space research this is particularly attractive, since it has mass and cost benefits in spacecraft design in that by using denser materials smaller detection systems can be fabricated without losing spectral acuity. Finally, unlike Si and Ge whose electronic and chemical properties are "fixed", those of compound semiconductors can be modified by band-gap engineering.
|Band gap energy
|Elemental Group IVB||Binary IV-IV Compounds||Binary III-V Compounds||Binary II-VI Compounds|
|2.25-2.50||GaP, AlP||ZnTe, CdS|
|Band gap energy
|Binary IV-VI Compounds||Binary n-VIIB Compounds||Ternary Compounds|
|0.25-0.50||PbSe, PbS, PbTe|
|1.75-2.00||CdZnTe, CdZnSe, InAlP|
|2.25-2.50||PbI2||TlBrI, InAlP, TlPbI3|
In principal compound semiconductors can also be matched to (a) specific applications or (b) specific environments. As an example of (a), we note that GaAs would be an ideal material for use in planetary X-ray fluorescent spectrometers or solar X-ray monitors, since, unlike silicon, gallium and arsenic do not occur naturally in the source spectra and both the Ga and As absorptions edges lie well outside the energy range of interest. This makes the interpretation of spectra considerably easier. Other suitable materials include CdTe and PbI2. With regard to (b), materials can be selected to operate at elevated temperatures, in harsh radiation environments or even in corrosive atmospheres.