Deep level defects in proton radiated GaAs grown on metamorphic SiGe∕Si substrates

Abstract

The effect of 2MeV proton radiation on the introduction of deep levels in GaAs grown on compositionally graded SiGe∕Si substrates was investigated using deep level transient spectroscopy (DLTS). Systematic comparisons were made with identical layers grown on both GaAs and Ge substrates to directly assess the influence of threading dislocations on radiation-related deep levels for both n-type and p-type GaAs. DLTS revealed that for p+n structures, proton irradiation generates electron traps at Ec−0.14eV, Ec−0.25eV, Ec−0.54eV, and Ec−0.72eV in the n-GaAs base, and, for n+p structures, radiation-induced hole traps appear at Ev+0.18eV, Ev+0.23eV, Ev+0.27eV, and Ev+0.77eV in the p-type GaAs base, irrespective of substrate choice for both polarities. The primary influence of substituting SiGe∕Si substrates for conventional GaAs and Ge substrates is on the introduction rates of the individual traps as a function of proton radiation fluence. Substantially reduced concentrations are found for each radiation-induced hole trap observed in p-type GaAs, as well as for the Ec−0.54eV trap in n-GaAs for samples on SiGe∕Si, as a function of proton fluence. Calculated trap introduction rates reveal reductions by as much as ∼40% for certain hole traps in p-GaAs grown on SiGe∕Si. This increased radiation tolerance for GaAs grown on SiGe∕Si is attributed to interactions between the low density (∼106cm−2) of residual dislocations within the metamorphic GaAs∕SiGe∕Si structure and the radiation-induced point defects. Nevertheless, the fact that the impact of dislocations on radiation tolerance is far more dramatic for n+p GaAs structures compared to p+n structures, may have implications on future III-V∕Si space solar cell design optimization, since end-of-life versus beginning-of-life differences are critical factors for power profiling in high radiation environments.

Epitaxial growth of highly mismatched III-V materials on (001) silicon for electronics and optoelectronics

“…Insertion of dislocation ilter layers, such as a strained layer superlattice [44] or thin strained layers [45], can facilitate the annihilation of threading dislocations thereby minimize intrusion of dislocations in the active layers of interest. Growth of compositionally graded bufers (e.g., SiGe, GaAsP) [46][47][48] to bridge the lattice constant between Si and GaAs is another approach that has been heavily investigated. Achieving high strain relaxation while maintaining a low threading dislocation density are igures of merit of such metamorphic graded bufers.…”

Electron and Proton Radiation Effects on Band Structure and Carrier Dynamics in MBE and MOCVD Grown III-V Test Structures

“…The absence of this effect in the proton exposed MBE n -type samples can be explained if the majority of exciton recombination events occur at the bandedge or at shallow sub bandgap donor states. Hydrogen ions passivate shallow donor states in GaAs, possibly by the direct bonding of the hydrogen to the donor atom [5], but such passivation was not evident from the SSPL analysis.…”

Modeling Electrochemical Etching of Proton Irradiated p-GaAs for the Design of MEMS Building Blocks

“…Many studies have been carried out in order to understand the nature of such defects leading to insulating GaAs and their influence on the electrical properties of irradiated GaAs substrates [8], [14], [16]- [19]. The decrease in conductivity, and in our particular electrochemical etching case the decrease in hole conduction, has been shown to be due to trapping of holes at specific trap centers [18], [20]. Such traps are created due to nuclear energy loss and it is thus obvious to relate the experimental defect production rate to the one calculated with e. g. SRIM [21], as shown in the past.…”