Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (B150 Gauss) and nuclear spin polarization (B15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in o5 ms at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications.
Optically detected magnetic resonance ͑ODMR͒ studies of molecular beam epitaxial GaNP/GaP structures reveal presence of a P-related complex defect, evident from its resolved hyperfine interaction between an unpaired electronic spin ͑S =1/ 2͒ and a nuclear spin ͑I = 1 2 ͒ of a 31 P atom. The principal axis of the defect is concluded to be along a ͗111͘ crystallographic direction from angular dependence of the ODMR spectrum, restricting the P atom ͑either a P Ga antisite or a P i interstitial͒ and its partner in the complex defect to be oriented along this direction. The principal values of the electronic g tensor and hyperfine interaction tensor are determined as: g Ќ = 2.013, g ʈ = 2.002, and A Ќ = 130ϫ 10 −4 cm −1 , A ʈ = 330ϫ 10 −4 cm −1 , respectively. The interface nature of the defect is clearly manifested by the absence of the ODMR lines originating from two out of four equivalent ͗111͘ orientations. Defect formation is shown to be facilitated by nitrogen ion bombardment under nonequilibrium growth conditions and the defect is thermally stable upon post-growth thermal annealing.
The origin of the two emission peaks located at ~242 nm and ~282 nm from Al 0.65 Ga 0.35 N/AlN multiple quantum wells (MQWs) structure with Al 0.75 Ga 0.25 N caplayer excited by an electron beam are investigated by using depth cathodoluminescence techniques. We observed an enhancement of deep-ultraviolet emission peak (~282 nm) intensities from MQWs by Mg doping . OCIS codes: (000.0000) General; (250.0250) Optoelectronics. Ultraviolet lights have been widely used in biomedical research, photolithography and sterilization. However, the traditional ultraviolet light sources have the disadvantages of the low emission efficiency, large structures and the presence of toxic constituents. Thus, a variety of concepts and constructions for the ultraviolet lights source, represented by AlGaN light-emitting diodes (LED) and laser diodes attracts many attentions[1-6]. Al x Ga 1-x N which has the tunable band gap by changing Al composition x, and theoretically its emission can cover wavelengths range from 210 to 365 nm. However, due to its poor crystal quality[7, 8] and low hole concentration[5], the high efficient and high power LEDs are difficult to be realized. Alternatively, Oto et al.[9]has used electron-beam excitation in an AlGaN/AlN multiple quantum-wells structure (MQWs) to achieve ~240 nm emission with an pretty high optical power and efficiency. This method is a milestone for realizing next high power and high efficient ultraviolet sources. Shimahara et al reported that emission intensity of Si-doped AlGaN film was significantly improved, which suggests doping may further improve the emission intensities[10].Thus in this study, we designed and fabricated Mg-doped in AlGaN/AlN MQWs and observed an enhancement of the deep-ultraviolet light emission (at ~280 nm) efficiency.Fig. 1b shows the SEM images of the cross section of the Mg-doped AlN based AlGaN/AlN MQWs structure. The Al 0.65 Ga 0.35 N/AlN-eight-period multiple quantum wells (MQWs) was grown on the buffer bilayers. The thickness of Al 0.65 Ga 0.35 N well and AlN barrier were 1 nm and 15 nm, respectively. The covering bilayers of AlN/ Al 0.75 Ga 0.25 N, with respective thickness of 300nm and 100nm, were fabricated on the MQWs. Fig. 1a presents the cathodoluminescence (CL) and transmission spectrum of the fabricated Mg doped device which shown two obvious emission peaks at the wavelength of ~242 nm and ~282 nm, respectively. The comparisons between the CL and transmission spectra indicates that the two peaks of ~242 nm and ~282 nm are from Al 0.75 Ga 0.25 N layer and AlGaN/AlN MQWs, respectively. The CL spectra image at 242 nm of the device across section was shown on Fig. 1c.Careful comparison between the SEM image (Fig. 1b) and the CL spectra image (Fig. 1c) reveals that the peak at ~242 nm, depicted in Fig. 1a, was from the band-edge emission of the Al 0.75 Ga 0.25 N layer.
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