Electrical Deep Level Transient Spectroscopy Research Articles

Deep level spectroscopy of high-power laser diode arrays

Deep defect centers in high-power AlGaAs/GaAs laser diode arrays emitting at a wavelength of 808 nm are studied by Fourier-transform photocurrent spectroscopy and by electrical deep level transient spectroscopy. Different types of deep centers with binding energies between 0.15 and 0.8 eV are found in graded-index and step-index diode structures. In all structures, the defect concentration increases with operation time. We demonstrate that different operation conditions of the devices, such as regular operation or accelerated aging at increased temperatures, cause different scenarios of deep level creation. In addition to deep centers, aging leads to the formation of shallow defects and a reshaping of the absorption band edge.

Characterization of traps in GaAs/W Schottky diodes by optical and electrical deep-level transient spectroscopy methods

Both the electrical and optical deep-level transient spectroscopy (DLTS) measurement methods were used to investigate the deep traps in GaAs that originate from the impurities included in the Schottky metal on GaAs/W Schottky diodes. Two distinct electron traps (E1 and E2, whose activation energies EA were, respectively, 0.65 and 0.58 eV) were detected by electrical DLTS in samples annealed at 650 °C. The variation of EA and trap density with changes in the Schottky barrier height indicates that the trap E1 can be identified with the EL2 usually observed in the GaAs grown by metalorganic chemical-vapor deposition. In addition, the trap E2 is found to be due to impurities that diffused from the W film into the GaAs layer during annealing. Four hole traps with activation energies of 0.76, 0.55, 0.43, and 0.30 eV were detected by optical DLTS in samples annealed at 650 °C. Comparison of the EA for each hole trap with data previously reported indicates that the first three traps are due to the transition metals Cr, Fe, and Cu, and that the last one is due to a native defect. These metals are confirmed from secondary-ion-mass spectroscopy analysis to be included in the as-deposited W film. Furthermore, these traps are also observed in GaAs permeable base transistors with the buried W gate.

Effects of secondary laser illumination during the transient measurement in optical and electrical deep level transient spectroscopy

To separate the majority and minority carriers in the deep level transient spectroscopy (DLTS), the transient is usually measured in the dark. However, under some circumstances, the transient measurement should be performed under illumination. In these cases, the effects introduced by the illumination become a concern. In this letter, effects of secondary laser illumination on samples of hydrogenated amorphous silicon (a-Si:H) during the transient measurement in optical and electrical DLTS are reported. The experimental results show that background illumination decreases the time constant of the transient but it is unlikely to create new gap states during the short time period.