Semiconductor nanowires studied by photocurrent spectroscopy

Abstract

Photocurrent spectroscopy is a versatile technique to identify and understand the optoelectronic dynamics occurring in semiconductor nanowires. Conventional photocurrent spectroscopy allows to explore the morphology and material properties of nanowires as well as their contact interfaces. Using time-resolved photocurrent spectroscopy one gets additional information on the multiple photocurrent generation mechanisms and their respective timescales. This chapter discusses various aspects of the photocurrent spectroscopy and it summarizes the physical mechanisms behind the photocurrent and photoconductance effects in semiconductor nanowires.

Ultrafast Photodetection in the Quantum Wells of Single AlGaAs/GaAs-Based Nanowires

“…Intriguingly, the sign of this contribution does not change equally when the exciting laser is scanned across the nanowire (Figure a and b). This contribution is consistent with a photothermoelectric current generated at the nanowire base ,, with Δ T the local temperature increase, R the total resistance of the electrical circuit, and S Nanowire ( S stripline ) the Seebeck coefficient of the nanowire (Ti/Au contact). At the nanowire base, a direct interface exists to the electron bath in the metal contact.…”

“…The contacts form lateral, coplanar strip lines with a total length of ∼58 mm, a width of 5 μm, and a separation of 6 μm. The strip lines are needed to perform the time-resolved photocurrent experiments, − which are discussed below. Due to the nanowire composition, two different metal/nanowire contacts are formed: (i) At the nanowire base (white triangle in Figure c), the GaAs core and the QWs are in direct contact to the Ti/Au.…”

“…The transients run along the strip lines, and they are detected on-chip by a time-delayed optical femtosecond probe pulse in combination with an Auston switch . We use ion-implanted amorphous silicon for this ultrafast photodetector with a time-resolution of about 1 ps. ,− The current I Sampling across the Auston-switch is sampled as a function of the time-delay Δ t between the two laser pulses, and it is directly proportional to the ultrafast photocurrents in the nanowire. − Hereby, the photocurrents in the nanowire can be measured with a picosecond time-resolution. Figure a and b shows I Sampling vs Δ t for resonant excitation of the GaAs core (Figure a with E laser = 1.53 eV at T bath = 8 K and Figure b with E laser = 1.42 eV at T bath = 296 K).…”

Optical Control of Internal Electric Fields in Band Gap-Graded InGaN Nanowires

“…So far, the time scales of the photocurrent response in InGaN nanowires are reported to be in the second to millisecond regime . From time-resolved photocurrent measurements on GaAs and InAs nanowires, it is known that electric fields, also present in our InGaN nanowires, can generate an ultrafast displacement current in the picosecond regime . We perform picosecond time-resolved photocurrent measurements, as described previously (Supporting Information) , to verify such an ultrafast photocurrent in the graded InGaN nanowire.…”