Double correlation technique (DDLTS) for the analysis of deep level profiles in GaAs and GaAs0.6P0.4

A very sensitive measurement technique is presented which can be applied to determine deep level profiles in space charge layers of Schottky barriers and p-n junctions of devices. The method uses a transient capacitance technique with correlation similar to Lang's DLTS (Deep Level Transient Spectroscopy). The DLTS technique is extended to double correlation DDLTS by relating the transient capacitance signals of two pulses, having different amplitudes, to reduce the measurement noise and to define an observation window for deep level profiling. Profiles can be determined for deep levels at concentrations 10
⁴
times lower than the background doping. Deep level profiles are presented for epitaxial GaAs and GaAs
0.6
P
0.4
. The profiles are taken in the bulk of the epilayer and in the region near the interface to the substrate for GaAs. In the bulk of the epilayer, one major deep level is observed at 0.18 eV below the conduction band. Near the interface, two levels appear in the epilayer at
E_{c} - E_{T} = 0.19
eV and
E_{c} - E_{T} = 0.43
eV with a density which increases towards the substrate. These levels can be explained by a silicon-oxygen complex, In GaAs
0.6
P
0.4
two major levels at 0.23 eV and 0.06 eV are observed. The spectrum taken for an LED, fabricated from this material, shows the same structure.