Non-destructive measurement of photoexcited carrier transport in graphene with ultrafast grating imaging technique

Abstract

Graphene has great potential for fabrication of ultrafast opto-electronics, in which relaxation and transport of photoexcited carriers determine device performance. Even though ultrafast carrier relaxation in graphene has been studied vigorously, transport properties of photoexcited carriers in graphene are largely unknown. In this work, we utilize an ultrafast grating imaging technique to measure lifetime (τ r), diffusion coefficient (D), diffusion length (L) and mobility (µ) of photoexcited carriers in monoand multi-layer graphene non-invasively. In monolayer graphene, D~10,000cm 2 /s and µ~120,000cm 2 /Vs have been observed, both of which decrease drastically in multilayer graphene, indicating that the remarkable transport properties in monolayer graphene originate from its unique Dirac-Cone energy structure. Mobilities of photoexcited carriers measured here are several times larger than the Hall and Field-Effect mobilities reported in literature (<15,000cm 2 /Vs), due to the high energy of photoexcited carriers. Our results indicate the importance of obtaining monolayer graphene to realize high-performance graphene devices, as well as the necessity to use transport properties of photoexcited carriers for predicting the performance of graphene-based opto-electronics.

Three-Dimensional Dirac Semimetal/Organic Thin Film Heterojunction Photodetector With Fast Response and High Detectivity

“…For our photodetector based on p-n heterojunction, there are three main reasons for the fast response speed: (1) The vertical heterojunction structure has intrinsically short transport length for carriers [45]. (2) The strong build-in electric field from the DSM and PbPc thin film can greatly facilitate the separation and collection of the photocarriers, inducing the high response speed [46,47]. (3) Moreover, when the heterojunction is applied with reverse bias voltage, the electric field caused by reverse bias is consistent with the build-in electric field, so the barrier height is enhanced.…”

“…Since the successful preparation of graphene in 2004 [1], graphene has been widely studied due to its excellent carrier transport performance, unique two-dimensional (2D) energy dispersion, and stable electrical and optical properties [2][3][4]. At present, graphene has shown extremely high application value in many fields such as photoelectric detection, solar cell and optical modulator [5][6][7][8][9][10][11].…”

Contactless photomagnetoelectric investigations of 2D semiconductors

“…It was experimentally shown that the carrier lifetime only decreases slightly with carrier density in graphene [ 7 ]. Taking into account this approximation and the known value of the carrier mobility at the Dirac point (determined from Van der Pauw measurements), the data presented in Fig.…”

“…The application of two-dimensional (2D) materials in electronic devices [ 1 – 6 ] requires the development of appropriate measurement methods for determining their typical semiconductor parameters, i.e., carrier mobility (μ) and lifetime (τ). Among these methods, contactless techniques [ 7 – 8 ] and mobility extraction methods based on field-effect measurements [ 9 ] are of great importance. Here we show a contactless method for determining these parameters in 2D semiconductors that is based on the photomagnetoelectric (PME) effect [ 10 ].…”

In-plane Thermal Conductivity Measurement with Nanosecond Grating Imaging Technique

“…The experimental setup of NGI is very simple because we monitor the temperatureinduced probe reflectivity change instead of diffraction. Recently, we implemented the same grating imaging technique into our femtosecond pump-probe spectrometer to detect carrier diffusion in graphene [31] and GaAs/AlAs SLs [32]. Our new technique is developed based on ns-TDTR due to its several advantages compared with an fs-TDTR.…”