Impact of dislocations on minority carrier electron and hole lifetimes in GaAs grown on metamorphic SiGe substrates

Abstract

The minority carrier lifetime of electrons (τn) in p-type GaAs double heterostructures grown on GaAs substrates and compositionally graded Ge/Si1−xGex/Si (SiGe) substrates with varying threading dislocation densities (TDDs) were measured at room temperature using time-resolved photoluminescence. The electron lifetimes for homoepitaxial GaAs and GaAs grown on SiGe (TDD∼1×106 cm−2) with a dopant concentration of 2×1017 cm−3 were ∼21 and ∼1.5 ns, respectively. The electron lifetime measured on SiGe was substantially lower than the previously measured minority carrier hole lifetime (τp) of ∼10 ns, for n-type GaAs grown on SiGe substrates with a similar residual TDD and dopant concentration. The reduced lifetime for electrons is a consequence of their higher mobility, which yields an increased sensitivity to the presence of dislocations in GaAs grown on metamorphic buffers. The disparity in dislocation sensitivity for electron and hole recombination has significant implications for metamorphic III-V devices.

III–V Multijunction Solar Cell Integration with Silicon: Present Status, Challenges and Future Outlook

“…Detailed investigation on the impact of TDs on the minority carrier lifetimes revealed superior dislocation tolerance for holes in n-type GaAs (τ p~1 0 ns) in comparison to electrons in p-type GaAs (τ n~1 .5 ns) material for a similar dislocation density and doping concentration (Carlin et al 2000;Andre et al 2004). The reduced electron lifetime was attributed to their higher mobility which translated to increased sensitivity toward the dislocations in GaAs layers grown on metamorphic SiGe buffers (Andre et al 2004).…”

“…The reduced electron lifetime was attributed to their higher mobility which translated to increased sensitivity toward the dislocations in GaAs layers grown on metamorphic SiGe buffers (Andre et al 2004). Such sensitivity of minority carrier lifetime in the metamorphic GaAs material on Ge/SiGe/Si substrates led to superior performance for p þ /n diodes over their n þ /p counterparts, and hence the p/n solar cell showed higher V oc compared to n/p solar cell (0.98 V vs 0.88 V) at a TDD~1 Â 10 6 cm −2 , indicating device polarity dependence for metamorphic GaAs solar cells grown on SiGe substrates Ringel et al 2003).…”

III-V Device Integration on Silicon Via Metamorphic SiGe Substrates

“…SJ GaAs solar cell structures were grown by MOCVD after deposition of a 0.1 µm GaAs nucleation layer by MBE on the SiGe substrates as previously discussed. Further details concerning the influence of MOCVD over growth on the MBE initiation layers can be found elsewhere (14,15). The GaAs and In 0.49 Ga 0.51 P layers were grown at a substrate temperature of 620°C, a growth rate ~ 2 µm/hr, and a V/III ratio of 100.…”

Ultra-high frequency photoconductivity decay in GaAs/Ge/GaAs double heterostructure grown by molecular beam epitaxy

“…Germanium has received significant attention for low-cost and high-density near infra-red detection, [1][2][3] template for heteroepitaxy of GaAs on Si for laser and solar cells, [4][5][6] multijunction solar cells, 7 tunnel transistors, 8 and high hole mobility p-channel material for next generation low-power metal-oxide field effect transistors on Si. 9 In addition, high-quality Ge/ GaAs heterostructure opens up the possibility of heterogeneous integration of photonic devices in the 1.3-1.5 lm range.…”

“…Moreover, Ge epitaxial film on a large bandgap GaAs material is of immense interest due to lattice-match (mismatch $0.07%), which ensures larger critical thickness, lower defect density, and strain-free Ge epitaxial film. To obtain the level of material quality necessary for minority carrier device applications, [1][2][3][4][5][6][7][10][11][12] it is necessary to grow defect-free GaAs/ Ge/GaAs double heterostructures (DHs) with high minority carrier lifetime and thin top GaAs layer on Ge that can be used as interface passivation layer for integration of high-k dielectric in order to achieve Ge-based CMOS logic. Recently, minority carrier lifetimes in bulk Ge, [13][14][15] Ge on GaAs, 16 and Ge on Si 17 were studied by several researchers since the carrier lifetime is one of the most important semiconductor parameters that is sensitive to the structure, density of crystal defects, and doping density in the semiconductor.…”