Photoconductivity measurements and trap analysis of wide bandgap nitride semiconductors

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-E_A/kT)). From the value of E_A ~ 1.0 eV the main defect in the unintentionally doped GaN sample (see Figure 2 left) can be assumed to be C_N.