Haowen Xi

Photoluminescence lineshape of ZnO

The merger of the absorption coefficient dispersion, retrieved from transmission by the modified Urbach rule introduced by Ullrich and Bouchenaki [Jpn. J. Appl. Phys. 30, L1285, 1991], with the extended Roosbroeck-Shockley relation reveals that the optical absorption in ZnO distinctively determines the photoluminescence lineshape. Additionally, the ab initio principles employed enable the accurate determination of the carrier lifetime without further specific probing techniques.

Photocurrent limit in nanowires.

Square root photocurrent dependences of nanowires on light intensity were reported in the literature without clarification of the limiting effect. In this Letter, we derived a relation excellently fitting the observed nonlinearities and, intensifying the significance of the result, we demonstrated that the fit parameters involved can be employed to determine the impurity concentration and electronic response time of nano-sized semiconductors.

Inherent photoluminescence Stokes shift in GaAs.

The intrinsic photoluminescence Stokes shift, i.e., the energy difference between optical band gap and emission peak, of 350 μm thick semi-insulating GaAs wafers is found to be 4 meV at room temperature. The result is based on the determination of the optical bulk band gap from the transmission trend via modified Urbach rule whose result is confirmed with the transmission derivative method. The findings reveal the detailed balance of the optically evoked transitions and disclose the intrinsic link between Stokes shift and the Urbach tail slope parameter.

Photocurrent theory based on coordinate dependent lifetime

Recent work by Pejova [Mater. Res. Bull. 43, 2887 (2008)] showed that the widely cited classical photocurrent theory of DeVore [Phys. Rev. 102, 86 (1956)] does not necessarily apply for photocurrent experiments carried out on thin-film semiconductors. In this Letter, we theoretically and experimentally justify the successful use of the photocurrent model published by Bouchenaki et al. [J. Opt. Soc. Am. B 8, 691 (1991)].

Relation between Debye temperature and energy band gap of semiconductors

The work addresses an unresolved topic in solid-state physics, i.e., the dependence of the Debye temperature (TD) on the energy band gap (Eg) of semiconducting materials. The systematic calculation of TD by using the ratio of sound velocity and lattice constant from the literature resulted in the relation TD∝exp(Eg). The exponential relationship is confirmed by a theoretical model based on the microscopic analysis of the electrical conductivity in metals and semiconductors.

Photoluminescence limiting of colloidal PbS quantum dots

The exposure of colloidal 2u2009nm PbS quantum dots to growing continuous wave laser excitation at 532u2009nm increases the photoluminescence intensity with the square root of the optical stimulus. The results herein in conjunction with previous findings [B. Ullrich and H. Xi, Opt. Lett. 38, 4698 (2013)] advocate the square root trend to be the general limiting function for photo-carrier transport and emission of optically excited nano-sized materials. We further show that the excitation of one electron-hole pair per quantum dot defines the saturation threshold for photoluminescence intensity and dynamic band filling.

The thermo-electric nature of the Debye temperature

The Debye temperature is typically associated with the heat capacity of a solid and the cut-off of the possible lattice vibrations, but not necessarily to the electric conductivity of the material. By investigating III-V and II-VI compound semiconductors, we reveal that the Debye temperature represents a thermo-electric material parameter, connecting the thermal and electronic properties of a solid via a distinct power law.

Theoretical Analysis of the Spectral Photocurrent Distribution of Semiconductors

Measurements of semiconductor photocurrent (PC) spectra have a long and rich history. During the 1960s and 1970s, the topic became one of the most studied phenomena in semi‐ conductor research so that entire textbooks were dedicated to the subject [1-4]. In spite these considerable activities, only a few theoretical efforts were published in order to fit PC spec‐ tra. The first attempt is attributed to DeVore [5], who, with the purpose to find an explana‐ tion for the typically measured PC peak in the vicinity of the band gap, presumed enhanced carrier recombinations at the semiconductor surface with respect to the bulk. In other words, along the light propagating coordinate the carrier lifetime (and therefore the recom‐ bination rate) is changing. However, instead to transfer this idea directly into a mathemati‐ cal model, DeVore used the non-measurable parameter carrier surface recombination velocity in order to achieve PC fits with a peak.