Determination of Free Electron Density in Sequentially Doped In_xGa_1-xAs by Raman Spectroscopy

Abstract

The advent and exponential growth of mobile computing has spurred greater emphasis on the adoption of III-V compound semiconductors in device architectures. The introduction of high charge carrier densities within InxGa1-xAs and the development of metrologies to quantitate the extent of doping have thus emerged as an urgent imperative. As an amphoteric dopant, Si begins to occupy anionic sites at high concentrations, thereby limiting the maximum carrier density that can be obtained upon Si doping of III-V semiconductors. Here, we present Raman results on sequentially doped In0.53Ga0.47As wherein sulfur monolayer doping is used to introduce additional carrier density to Si-doped samples. The sequential doping of Si and S allows for high carrier concentrations of up to 1.3 × 10(19) cm(-3) to be achieved without damaging the III-V lattice. The coupling of the plasmon in the doped samples to the longitudinal optic phonons allows Raman spectroscopy to serve as an excellent probe of the extent of dopant activation, charge carrier density, and the surface depletion region. In particular, the energy position of a high-frequency coupled mode (HFCM) that is detected above 400 cm(-1) is used to extract the free electron density in these samples. The extracted free electron densities are well correlated with measured sheet resistance values and the carrier densities deduced from Hall measurements.

Chemical approaches for doping nanodevice architectures

“…Most recently, Kort and co-workers reported a method of determining the free electron density in sequentially doped InGaAs using Raman spectroscopy [56]. Again, using the commonly-used ammonium sulfide treatment was used to passivate the InGaAs surface with S, and the substrate was for Ge nanowires doped using AsH 3 and PH 3 at 650 °C in the case of AsH 3 and 650 °C and 700 °C in the case of PH 3 .…”

Activation of Si implants into InAs characterized by Raman scattering

“…Previous authors have used Raman scattering to measure free carrier concentrations making use of the fact that LO phonons will readily couple with the plasma oscillations of free carriers in InAs and other polar, III-V materials. 13,14,[21][22][23][24][25][26][27] The L þ phonon-plasmon coupled mode is especially sensitive to changes in the carrier concentration at high n-type carrier concentrations in InAs where Raman shifts towards higher wavenumbers correspond to increasing free electron concentrations. Diffusion of Si in InAs beyond the initial implanted profile may increase the active sheet number measured by Hall effect precluding accurate carrier concentration estimates without corresponding Si diffusion data.…”

Liquid-Phase Monolayer Doping of InGaAs with Si-, S-, and Sn-Containing Organic Molecular Layers

“…There have been reports of direct bonding to oxide-free III–V surfaces using organic thiols, − and due to the simplicity of the procedure and availability of suitable commercial molecules, as well as the excellent oxidation resistance offered by III–V-thiol chemistry, this was one of the functionalization approaches used in this study. Solution-phase S doping of InGaAs has been relatively widely reported due to the simplicity of the procedure. − Ammonium sulfide is often used to remove the native oxides on InGaAs, but the process conveniently results in a S-terminated surface, allowing diffusion of S as a monolayer into the InGaAs surface via a rapid thermal anneal step. Although not a traditional MLD process, due to the gas-phase nature of the dopant precursor and high-vacuum requirements of the deposition process, Kong and co-workers recently reported the Si MLD of InGaAs nanostructures by means of a MOCVD-deposited silane layer with a thickness of a few monolayers .…”