Impact of excitation energy on hot carrier properties in InGaAs multi‐quantum well structure

Abstract

Hot carrier solar cells aim to overcome the theoretical limit of single‐junction photovoltaic devices by suppressing the thermalization of hot carriers and extracting them through energy selective contacts. Designing efficient hot carrier absorbers requires further investigation on hot carrier properties in materials. Although the thermalization of hot carriers is responsible for a large portion of energy loss in solar cells, it is still one of the least understood phenomena in semiconductors. Here, the impact of excitation energy on the properties of photo‐generated hot carriers in an InGaAs multi‐quantum well (MQW) structure at various lattice temperatures and excitation powers is studied. Photoluminescence (PL) emission of the sample is detected by a hyperspectral luminescence imager, which creates spectrally and spatially resolved PL maps. The thermodynamic properties of hot carriers, such as temperature and quasi‐Fermi‐level splitting, are carefully determined via applying full PL spectrum fitting, which solves the Fermi–Dirac integral and considers the band‐filling effect in the nanostructured material. In addition, the impact of thermalized power density and carrier scattering with longitudinal optical phonons on the spectral linewidth broadening under two excitation energies is studied.

The role of nonequilibrium LO phonons, Pauli exclusion, and intervalley pathways on the relaxation of hot carriers in InGaAs/InGaAsP multi-quantum-wells

“…In the present work, we first experimentally extract the carrier temperature in a type-I band alignment In 0.53 Ga 0.47 As/In 0.8 Ga 0.2 As 0.44 P 0.56 multi-quantum-well (MQW) structure from photoluminescence characterization illuminated by continuous-wave (CW) lasers at 405 nm (above the L valley) and at 980 nm (below the L valley). This MQW structure has previously shown evidence of robust hot-carrier effects at room temperature 25,26 . However, the origin of this exciting effect and the impact of hot phonons and intervalley scattering mechanisms have not been quantitatively studied.…”

“…The thermodynamic properties of emitting particles are determined by fitting the whole PL spectrum with the generalized Planck’s law, as described by 31 , 32 : where is the PL intensity, energy-dependent absorptivity, the speed of light, the Planck’s constant, the Boltzmann constant, and represents the difference of the quasi-Fermi levels of the electrons and holes ( ) under photo-excitation conditions. The details of the full spectrum fit are presented elsewhere 24 , 26 . The results of the full spectrum fit are shown by the black lines in Fig.…”

Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells

“…To determine the average temperature of hot carriers at each excitation power, the PL spectra are fitted with the generalized Planck’s law using the absorption method, which takes into account the change in the sample’s absorption due to band-filling and quantum confinement effects as well as the parasitic absorption induced by the optical setup. The details of this analysis method are reported elsewhere . Note also that the data are referred to as the real power density absorbed by the NW upon excitation, to allow a direct quantitative comparison of carrier temperature among different samples.…”

“…The details of this analysis method are reported elsewhere. 45 Note also that the data are referred to as the real power density absorbed by the NW upon excitation, to allow a direct quantitative comparison of carrier temperature among different samples. This is important because the level of photoabsorption by the NWs varies depending on their dimensions and the array spacing, inducing resonant light-trapping effects, which can result in even greater photoabsorption than in 2D planar structures.…”

“…Another mechanism that can contribute to the formation of hot carrier populations is Auger heating. ,, Through this process, the excess kinetic energy of an electron (or hole) is transferred to another particle, promoting it to higher energy states. Although this nonradiative interaction reduces the number of free carriers in the semiconductor, it can benefit hot carrier solar cells by creating hot populations .…”