A GaAs/GalnP dual junction solar cell grown by molecular beam epitaxy

We report the recent result of GaAs/GalnP dual-junction solar cells grown by all solid-state molecularbeam-epitaxy （MBE）. The device structure consists of a GaIn0.4sP homojunction grown epitaxially upon a GaAs homojunction, with an interconnected GaAs tunnel junction. A photovoltaic conversion efficiency of 27% under the AM1.5 globe light intensity is realized for a GaAs/GaInP dual-junction solar cell, while the efficiencies of 26% and 16.6% are reached for a GaAs bottom cell and a GaInP top cell, respectively. The energy loss mechanism of our GaAs/GalnP tandem dual-junction solar cells is discussed. It is demonstrated that the MBE-grown phosphide-containing Ⅲ-V compound semiconductor solar cell is very promising for achieving high energy conversion efficiency.     

0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices with compositionally undulating step-graded InAsyP1-y buffers

Single-junction,lattice-mismatched In0.69Ga0.31As thermophotovoltaic(TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition(MOCVD).Compositionally undulating stepgraded InAsyP1-y buffer layers with a lattice mismatch of ～1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate.With an optimized buffer thickness,the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion.High-performance single-junction devices are demonstrated,with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2,which are measured under the standard solar simulator of air mass 1.5-global(AM 1.5 G).     

Transparent conducting indium-tin-oxide (ITO) film as full front electrode in III-V compound solar cell

The application of transparent conducting indium-tin-oxide (ITO) film as full front electrode replacing the conventional bus-bar metal electrode in III-V compound GaInP solar cell was proposed. A high-quality, non-rectifying contact between ITO and 10 nm N⁺-GaAs contact layer was formed, which is benefiting from a high carrier concentration of the terrilium-doped N⁺-GaAs layer, up to 2×10¹⁹ cm^-3. A good device performance of the GaInP solar cell with the ITO electrode was observed. This result indicates a great potential of transparent conducting films in the future fabrication of larger area flexible III-V solar cell.     

In0.68Ga0.32As热光伏电池的制作和特性分析

用在InP衬底上失配生长的能隙为0.6eV的In0.68Ga0.32As制成了热光伏(TPV)电池。对其光伏特性的测试分析表明,通过对As组分渐变的InAsxP1-x缓冲层厚度的优化,可以将晶格失配引起的位错完全弛豫在缓冲层内,从而大幅改善热光伏电池的性能。在AM1.5G标准光谱下,与晶格失配没有被完全弛豫的热光伏电池相比,优化措施可将开路电压从0.19V提高到0.21V,外量子效率在长波处可达到85%,转换效率也提高了30%。     

基于分子束外延生长的1.05 eV InGaAsP的超快光学特性研究

利用分子束外延方法制备了应用于四结光伏电池的1.05 eV InGaAsP薄膜, 并对其超快光学特性进行了研究. 温度和激发功率有关的发光特性表明: InGaAsP材料以自由激子发光为主. 室温下InGaAsP材料的载流子发光弛豫时间达到10.4 ns, 且随激发功率增大而增大. 发光弛豫时间随温度升高呈现S形变化, 在低于50 K时随温度升高而增大, 在50–150 K之间时减小, 而温度高于150 K时再次增大. 基于载流子弛豫动力学, 分析并解释了温度及非辐射复合中心浓度对样品材料载流子发光弛豫时间S形变化的影响.     

Fabrication and Characterization of High Power InGaN Blue-Violet Lasers with an Array Structure

InGaN/GaN multi-quantum-well-structure laser diodes with an array structure are successfully fabricated on sapphire substrates. The laser diode consists of four emitter stripes which share common electrodes on one laser chip. An 800-μm-long cavity is formed by cleaving the substrate along the （1100） orientation using laser scriber. The threshold current and voltage of the laser array diode are 2A and 10.5 V, respectively. A light output peak power of 12 W under pulsed current injection at room temperature is achieved. We simulate the electric properties of GaN based laser diode in a co-planar structure and the results show that minimizing the difference of distances between the different ridges and the n-electrode and increasing the electrical conductivity of the n-type GaN are two effective ways to improve the uniformity of carrier distribution in emitter stripes. Two pairs of emitters on a chip are arranged to be located near the two n-electrode pads on the left and right sides, and the four stripe emitters can laser together. The laser diode shows two sharp peaks of light output at 408 and 409 nm above the threshold current. The full widths at half maximum for the parallel and perpendicular far field patterns are 8° and 32°, respectively.     

基于InP衬底的晶格失配In0.68Ga0.32As的MOCVD生长及其特性研究

采用MOCVD生长技术在InP衬底上成功实现了晶格失配的3μm In0.68 Ga0.32As薄膜生长.通过As组分的改变,利用张应变和压应变交替补偿的InAsxP1-x应变缓冲层结构来释放由于晶格失配所产生的应力,在InP衬底上得到了与In0.68Ga0.32 As晶格匹配的InAsxP1-x“虚拟”衬底,通过对缓冲层厚度的优化,使应力能够在“虚拟”衬底上完全豫弛.通过原子力显微镜(AFM)、高分辨XRD、透射电镜(TEM)和光致发光(PL)等测试分析表明,这种释放应力的方法能够有效提高In0.68 Ga0.32 As外延层的晶体质量.     

Room-Temperature Continuous-Wave Operation of InGaN-Based Blue-Violet Laser Diodes with a Lifetime of 15.6 Hours

We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing （FS） GaN substrate by metal organic chemical vapor deposition （MOCVD）. The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well （MQW）, respectively.     

Time delay in InGaN multiple quantum well laser diodes at room temperature

This paper reports that a long delay between the beginning of pumping current pulse and the onset of optical pulse is observed in InGaN laser diodes.The delay time decreases as the pumping current increases,and the speed of the delay time reduction becomes slower as the current amplitude increases further.Such delay phenomena are remarkably less serious in laser diodes grown on GaN substrate than those on sapphire.It attributes the delay to the traps which cause a large optical loss by saturable absorption and retard the laser action.The traps can be bleached by capturing injected carriers.The effect of GaAs laser irradiation on InGaN laser action demonstrates that the traps responsible for the delay are deep centres which can be filled by the photo-assisted processes.