C. Y. Jiang

Room-temperature spin photocurrent spectra at interband excitation and comparison with reflectance-difference spectroscopy in InGaAs/AlGaAs quantum wells

Spectra of the interband spin photocurrent due to Rashba and Dresselhaus spin splittings have been experimentally investigated in InGaAs/AlGaAs quantum wells at room temperature. The Rashba- and Dresselhaus-induced circular photogalvanic effect (CPGE) spectra are found to be quite similar in the spectral regions corresponding to the transitions 1e1hh (the first conduction to the first valence sub-band of heavy hole) and 1e2hh. The ratio of Rashba- and Dresselhaus-induced CPGE currents for the transition 1e1hh is estimated to be 4.95. The magnitude of the Rashba-induced CPGE current is up to several tens of nA/W for the transition 1e1hh, which is 1 order of magnitude larger than that obtained in GaN/AlGaN superlattices. Comparing the CPGE spectrum with reflectance-difference and photoreflectance spectra, we find that the large Rashba spin splitting is mainly induced by a large indium atom segregation effect and by the internal field in the quantum wells.

Observation of the photoinduced anomalous Hall effect spectra in insulating InGaAs/AlGaAs quantum wells at room temperature

The photocurrent spectra of inter-band photoinduced anomalous Hall effect (AHE) in insulating InGaAs/AlGaAs quantum wells have been observed at room temperature. The AHE current changes linearly with longitudinal electric fields. The anomalous Hall conductivity corresponding to excitonic state 1HH-1E (the first valence subband of heavy hole to the first conduction) has the same sign with that of excitonic state 1LH-1E, while the sign inverses when the photon energy is larger than the excitonic state 1LH-1E. The reason for this interesting phenomenon has been discussed. Due to the strong Rashba spin-orbit coupling in this perfect crystal, the photoinduced AHE is supposed to be intrinsic.

Helicity dependent photocurrent enabled by unpolarized radiation in a GaAs/Al0.3Ga0.7As two-dimensional electron system

We report the experimental observation of photo-assisted generation of helicity dependent photocurrents (PA-HDPC) in a GaAs/Al0.3Ga0.7As two-dimensional electron gas, which is distinct from the circular photogalvanic effect (CPGE). The PA-HDPC is generated under suppressed configuration of CPGE with the illumination of an obliquely incident unpolarized radiation in the system of C2v point group symmetry. We suggest that the PA-HDPC originates from spin-orbit coupling as well as the CPGE. The unpolarized assisted radiation, instead of the circularly polarized radiation, imposes an asymmetric distribution of the spin-polarized carriers in the system and results in a helicity dependent photocurrent.

Circular photogalvanic effect induced by near-infrared radiation in InAs quantum wires patterned quasi-two-dimensional electron system

In this letter we investigated the InAs/InAlAs quantum wires (QWRs) superlattice by optically exciting the structure with near-infrared radiation. By varying the helicity of the radiation at room temperature we observed the circular photogalvanic effect related to the C2v symmetry of the structure, which could be attributed to the formation of a quasi-two-dimensional system underlying in the vicinity of the QWRs pattern. The ratio of Rashba and Dresselhaus terms shows an evolution of the spin–orbit interaction in quasi-two-dimensional structure with the QWR layer deposition thickness.

In-plane optical anisotropy in GaAsN/GaAs single-quantum well investigated by reflectance-difference spectroscopy

The interface properties of GaNxAs1-x/GaAs single-quantum well is investigated at 80 K by reflectance difference spectroscopy. Strong in-plane optical anisotropies (IPOA) are observed. Numerical calculations based on a 4 band K . P Hamiltonian are performed to analyze the origin of the optical anisotropy. It is found that the IPOA can be mainly attributed to anisotropic strain effect, which increases with the concentration of nitrogen. The origin of the strain component epsilon(xy) is also discussed.

SUPERCONDUCTIVITY RELATED TO INDIUM-DIFFUSED GAAS

Superconductivity in an indium‐diffused GaAs system has been investigated by magnetic‐field‐modulated microwave absorption and ac susceptibility measurements. These show existence of a superconducting phase in some of the samples. Indium was used to solder GaAs on Mo holder or deposit on the surface of GaAs, following the different heat treatments. This indium‐diffused GaAs from surface or back side is most likely the origin of the superconductivity.

Intrinsic photoinduced anomalous Hall effect in insulating GaAs/AlGaAs quantum wells at room temperature

The photocurrent spectra of the inter-band photoinduced anomalous Hall effect (PAHE) in insulating GaAs/AlGaAs quantum wells have been observed at room temperature. The PAHE current changes linearly with the varied longitudinal electric fields. The anomalous Hall conductivity corresponding to excitonic state 1HH-1E (the first valence subband of heavy hole to the first conduction) has the same sign with that of excitonic state 1LH-1E (the first valence subband of light hole to the first conduction), while under uniaxial strain along the ⟨110⟩ axes, they have different signs. The PAHE current of 1HH-1E decreases linearly, but that of 1LH-1E increases linearly with shear strain. The linearly dependence of the PAHE current on uniaxial strain along the ⟨110⟩ axes suggests that the dominant mechanism is intrinsic, which has not yet been confirmed in our previous work [Yu et al., Appl. Phys. Lett. 100, 142109 (2012)].

Detecting and tuning anisotropic mode splitting induced by birefringence in an InGaAs/GaAs/AlGaAs vertical-cavity surface-emitting laser

The mode splitting induced by birefringence in an InGaAs/GaAs/AlGaAs vertical-cavity surface-emitting laser (VCSEL) has been studied by reflectance difference spectroscopy (RDS) at room temperature. The mode splitting, anisotropic broadening width, and the anisotropic integrated area of the cavity mode are determined. Uniaxial strain on the order of 10−4 is introduced to tune the mode splitting. The mode splitting can be linearly tuned by the uniaxial strain, which agrees very well with theoretical calculations using a Jones matrix approach. We demonstrate that the RDS is a powerful, nondestructive tool to study the cavity anisotropy of VCSELs.

Observation of strong anisotropic forbidden transitions in (001) InGaAs/GaAs single-quantum well by reflectance-difference spectroscopy and its behavior under uniaxial strain

AbstractThe strong anisotropic forbidden transition has been observed in a series of InGaAs/GaAs single-quantum well with well width ranging between 3 nm and 7 nm at 80 K. Numerical calculations within the envelope function framework have been performed to analyze the origin of the optical anisotropic forbidden transition. It is found that the optical anisotropy of this transition can be mainly attributed to indium segregation effect. The effect of uniaxial strain on in-plane optical anisotropy (IPOA) is also investigated. The IPOA of the forbidden transition changes little with strain, while that of the allowed transition shows a linear dependence on strain. PACS 78.66.Fd, 78.20.Bh, 78.20.Fm

Excitation wavelength dependence of the anomalous circular photogalvanic effect in undoped InGaAs/AlGaAs quantum wells

The excitation wavelength dependence of the anomalous circular photogalvanic effect (ACPGE) current arising from the reciprocal spin Hall effect (RSHE) in undoped InGaAs/AlGaAs quantum wells is measured under normal incidence of circularly polarized light at room temperature. We found that the spot location with the maximum ACPGE current is wavelength independent. And the normalized ACPGE current decreases at smaller wavelengths, which can be attributed to the sharp decrease of the spin relaxation time (τs) and the hot electron relaxation time (τ1) at smaller wavelengths. The study of the excitation wavelength dependence of ACPGE current is a good supplement to the in-depth investigation of RSHE.