Equipped with a 355 nm laser (μ-PCD) or a 375 nm laser diode (MDP), the MDPmap as well as the MDpicts from Freiberg Instruments are suitable for photoconductivity measurements and trap analysis on wide-bandgap nitride semiconductors. The homogeneity of n-type doping can be analyzed by means of the photoconductivity (signal height). It is strongly dependent on the resistivity and the carrier lifetime.
The usually long apparent lifetimes are caused by trapping centers in the samples. Deep traps in wide-bandgap semiconductors can be investigated by MDpicts in the temperature range from 30 K up to 800 K. Compared to related methods (e.g. DLTS), MDpicts is a contactless and nondestructive method which also allows the investigation of highly n-doped semiconductors. The trap activation energy can be determined from the slope of the Arrhenius plot or estimated by directly fitting the lifetime reduction as a function of temperature by τ(T)= τ0/((1+aexp-EA/kT)). From the value of EA ~ 1.0 eV the main defect in the unintentionally doped GaN sample (see Figure 2 left) can be assumed to be CN.
Figure 1: Photoconductivity maps measured by MDP of four different Si doping concentrations in GaN layers.
Figure 2: Examples of the MDpicts time constants as a function of inverse temperature for left an unintentionally doped GaN sample and right a Si-doped GaN sample.
Related Solutions and Industries: Epitaxial Layers & Thin Films
