生长温度对立方MgZnO薄膜生长取向和紫外光吸收特性的影响

利用脉冲激光沉积技术在非晶石英衬底上制备立方结构MgZnO薄膜,并研究MgZnO薄膜结晶特性、光学带隙随生长温度的变化情况。当生长温度从150℃升高到700℃时,MgZnO薄膜的生长取向由（200）向（111）转变。在600℃以下,MgZnO薄膜光学带隙的变化规律与晶格中Mg和Zn原子比例的变化趋势是一致的;而当温度升至700℃时,虽然MgZnO晶格中Mg和Zn原子比例降低,但由于平均晶粒尺寸变大,薄膜的光学带隙反而上升。在300℃和700℃晶格匹配的情况下,获得了单一（200）和（111）取向的立方MgZnO薄膜。     

Direct-current piezoelectric nanogenerator based on p-Si/n-ZnO heterojunction

We have demonstrated a direct-current piezoelectric nanogenerator with a novel structure of p-Si/n-ZnO heterojunction. Low resistance p-type silicon chip, with a large number of nano-concaves on the surface, was utilized as a top electrode over the n-type ZnO nanorod arrays, forming a heterojunction nanogenerator. Piezoelectric current, with average singles about 1 nA, was generated from the heterojunction nanogenerator. Rectifying behavior of the p-Si/n-ZnO heterojunction in our piezoelectric nanogenerator was analyzed from the I–V curve and the energy band structure. Furthermore, output tests of reverse connection and two devices parallel connection clearly eliminate the effects from measurement system errors and confirms that the current is generated from the nanogenerator. Our research presents an approach to integrating a new type of nanogenerator using the silicon chip directly, without expensive Pt or Au coated on the electrode surfaces.     

Au电极厚度对MgZnO紫外探测器性能的影响

利用分子束外延设备(MBE)制备了MgZnO薄膜.X射线衍射谱、紫外-可见透射光谱和X射线能谱表明薄膜具有单一六角相结构,吸收边为340 nm,Zn/Mg组分比为62:38.采用掩膜方法使用离子溅射设备,在MgZnO薄膜上制备了Au电极,并实现了Au-MgZnO-Au结构的紫外探测器.通过改变溅射时间,得到具有不同Au电极厚度的MgZnO紫外探测器.研究结果表明:随着Au电极厚度的增加,导电性先缓慢增加,再迅速增加,最后缓慢增加并趋于饱和;而Au电极的透光率则随厚度的增加呈线性下降.此外,随着Au电极厚度的增加,器件光响应度先逐渐增大,在Au电极厚度为28 nm时达到峰值,之后逐渐减小.     

Effect of ambient temperature on electrical properties of nanostructure n-ZnO/p-Si heterojunction diode

The nanostructure n-ZnO/p-Si heterojunction diode was fabricated by sol–gel method. The structural and morphological properties of the nanostructure ZnO film have been investigated. The X-ray diffraction spectra indicated that the films are of polycrystalline nature. The scanning electron microscopy images indicate that the surface morphology of ZnO film is almost homogeneous and the ZnO film is consisted of the circular formed with coming together of the nanoparticles. The electrical characterization of nanostructure n-ZnO/p-Si heterojunction diode has been investigated by current–voltage characteristics. The ideality factor (n) of the diode was found for different ambient temperatures and the obtained 6.40 value for 296 K is higher than unity due to the interface states between the two semiconductor materials and series resistance. The values of n increased with decreasing ambient temperature. The reverse current of the diode increased with illumination intensity of 100 mW cm⁻² and the diode gave a maximum open circuit voltage V_oc of 0.19 V and short-circuits current I_sc of 8.03 × 10⁻⁸ A.     

Low-voltage blue light emission from n-ZnO/p-GaN heterojunction formed by RF magnetron sputtering method

High quality n-ZnO/p-GaN heterojunction was fabricated by growing highly crystalline ZnO epitaxial films on commercial p-type GaN substrates via radio frequency (RF) magnetron sputtering. Low-voltage blue light emitting diode with a turn-on voltage of ∼2.5 V from the n-ZnO/p-GaN heterojunction was demonstrated. The diode gives a bright blue light emission located at ∼460 nm and a low threshold voltage of 2.7 V for emission. Based on the results of the photoluminescence (PL) and electroluminescence (EL) spectra, the origins of the EL emissions were studied in the light of energy band diagrams of ZnO–GaN heterojunction, and may attribute to the radiative recombination of the holes in p-GaN and the electrons injected from n-ZnO, which almost happened on the side of p-GaN layer. These results may have important implications for developing short wavelength optoelectronic devices.     

The structure and optical characters of the ZnO film grown on GaAs/Al2O3 substrate

In this paper ZnO films are grown on GaAs/Al₂O₃ substrates at different temperature by metal-organic chemical vapor deposition (MOCVD). The GaAs/Al₂O₃ substrates are formed by depositing GaAs layer (∼35 nm) on the Al₂O₃ substrate. The results of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrate that most of the Ga and As atoms form Ga-As bond and the GaAs layer does not present any orientation. The characters of the ZnO films grown on GaAs/Al₂O₃ substrates are investigated by XRD, photoluminescence (PL), atomic force microscopy (AFM) and Raman scattering. Compared with ZnO film grown on Al₂O₃ substrate, ZnO film prepared by our fabrication scheme has good crystal and optical quality. Meanwhile its grain size becomes bigger according to the AFM image. Raman analysis indicates that the intrinsic defects and the in-plane tensile stress are obviously reduced in ZnO/GaAs/Al₂O₃ samples.     

Effect of emitter layer doping concentration on the performance of silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15 nm)/a-Si:H(10 nm)/ epitaxial c-Si(47 μm)/epitaxial c-Si(3 μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot-wire chemical vapour deposition. The effect of the doping concentration of emitter layer S_d (S_d=PH₃/(PH₃+SiH₄+H₂)) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S_d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S_d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm², a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

The barrier height inhomogeneity in Al/p-Si Schottky barrier diodes with native insulator layer

The current-voltage (I-V) characteristics of Al/p-Si Schottky barrier diodes (SBDs) with native insulator layer were measured in the temperature range of 150-375 K. The estimated zero-bias barrier height Φ_B0 and the ideality factor n assuming thermionic emission (TE) theory show strong temperature dependence. Evaluation of the forward I-V data reveals an increase of zero-bias barrier height Φ_B0 but decrease of ideality factor n with increase in temperature. The conventional Richardson plot exhibits non-linearity below 250 K with the linear portion corresponding to activation energy of 0.41 eV and Richardson constant (A^*) value of 1.3 × 10⁻⁴ A cm⁻² K⁻² is determined from intercept at the ordinate of this experimental plot, which is much lower than the known value of 32 A cm² K² for holes in p-type Si. Such behavior is attributed to Schottky barrier inhomogene ties by assuming a Gaussian distribution of barrier heights (BHs) due to barrier height inhomogeneities that prevail at interface. Also, Φ_B0 versus q/2kT plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of Φ_B0 = 1.055 eV and σ₀ = 0.13 V for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Thus, the modified versus q/kT plot gives Φ_B0 and A^* as 1.050 eV and 40.08 A cm⁻² K⁻², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 40.03 A cm⁻² K⁻² is very close to the theoretical value of 32 A K⁻² cm⁻² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I-V characteristics of the Al/p-Si Schottky barrier diodes with native insulator layer can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights.     

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15nm)/a-Si:H(10nm)/ epitaxial c-Si(47μm)/epitaxial c-Si(3μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer S d (Sd =PH3 /(PH3 +SiH4 +H2 )) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35mA/cm2 , a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

Electrical characterization of p-ZnO/p-Si heterojunction

Nitrogen doped p-ZnO film, with urea as nitrogen source, is fabricated by pulsed laser deposition on well-cleaned p-type (1 0 0) Si substrates. The structural and electrical properties of the p-p heterojunction are investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. It shows a diode-like behavior with turn-on voltage of 0.5 V. The ideality factor η determined by applying positive potential in p-ZnO and negative potential along p-Si is found to be 6. Such a high value of η is attributed to lattice mismatch between ZnO and Si. and other factors responsible are thermoionic emission, minority carrier injection and recombination. C-V results indicate an abrupt interface and a band bending of 0.9 V in the silicon. Heterojunction band diagram for p-ZnO/p-Si is proposed.     

Effect of GaInP intermediate barrier in 1.3 μm compressive-strained GaInAsP/GaInAsP multiple-quantum-wells laser diodes

In this article, 1.3 μm Ga_0.27In_0.63As_0.67P_0.33/Ga_0.11In_0.89As_0.24P_0.76 compressive-strain multiple-quantum-wells (CS-MQWs) with Ga_0.09In_0.91P intermediate barrier (IB) laser diodes (LDs) have been grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The photoluminescence (PL) measurement indicates that the CS-MQWs with 20 Å Ga_0.09In_0.91P IB have the narrowest full width at half maximum (FWHM) of 43.9 meV. The 55-μm-width metal contact and 900-μm cavity length as-cleaved broad-area LDs with the Ga_0.09In_0.91P IB have the better performance than those of LDs without Ga_0.09In_0.91P IB, including a threshold current density of 0.86 kA/cm², a differential quantum efficiency of 25.6%, an internal quantum efficiency of 50%, and an internal optical loss of 25 cm⁻¹. Finally, the GaInAsP/GaInAsP CS-MQWs with the Ga_0.09In_0.91P IB LDs were processed as 4-μm-width ridge and an as-cleaved 600-μm-cavity length. It exhibits a threshold current of 38.5 mA, a slope efficiency of 0.16 W/A, a characteristic temperature of 80.5 K, a maximum operating temperature up to 80 °C without power saturation, and a red-shift rate of 0.38 nm/°C, and a relaxation frequency response of 5.8 GHz. The 3-dB bandwidth for the LDs with GaInP IB is as high as 9 GHz without considering the damping factor and coupling loss.     

Effects of annealing treatment on the formation of CO2 in ZnO thin films grown by metal-organic chemical vapor deposition

Post-growth annealing was carried out on ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD). The grain size of ZnO thin film increases monotonically with annealing temperature. The ZnO thin films were preferential to c-axis oriented after annealing as confirmed by X-ray diffraction (XRD) measurements. Fourier transformation infrared transmission measurements showed that ZnO films grown at low temperature contains CO₂ molecules after post-growth annealing. A two-step reaction process has been proposed to explain the formation mechanism of CO₂, which indicates the possible chemical reaction processes during the metal-organic chemical vapor deposition of ZnO films.     

Electroluminescence of the p-ZnO:As/n-ZnO LEDs grown on ITO glass coated with GaAs interlayer

In this paper, we proposed a new p-type ZnO doping method with metal organic chemical vapor deposition (MOCVD) technology by inserting a GaAs interlayer between substrate and ZnO epitaxial layer. The doping concentration of p-type ZnO film is able to be controlled by adjusting the thickness of the GaAs interlayer. With this method, we fabricated n-ZnO/p-ZnO:As homojunction light-emitting diode (LED) on ITO-glass substrate pre-coated with 20 nm GaAs interlayer. The device exhibits a typical rectifying behavior by current-voltage (I-V) measurement. When the device is forward biased, UV-vis electroluminescence (EL) emissions can be observed clearly.     

Ga掺入对立方相MgZnO薄膜晶体结构的影响

采用金属有机物化学气相沉积方法生长了立方相Mg_0.56Zn_0.44O：Ga薄膜,Ga在MgZnO中的摩尔分数为2.8%~4.5%。低掺杂水平的MgZnO可以保持其良好的结晶特性。随着Ga元素的摩尔分数升高至3.1%、3.3%与4.5%,立方相MgZnO中分别出现了Ga₂O₃、ZnO与ZnGa₂O₄分相。其中,Ga₂O₃与ZnGa₂O₄相的出现是由于Ga的掺杂使这两相在MgZnO基质中饱和析出,而ZnO分相被归因于Ga的引入部分破坏了立方MgZnO的亚稳态结构状态,使组分原本就处于分相区的立方MgZnO出现相分离。     

氧气压强对PLD制备MgZnO薄膜光学性质的影响

使用准分子脉冲激光沉积(PLD)方法在Si(100)基片上制备了高度c轴取向的MgZnO薄膜。分别使用SEM、XRD、XPS、PL谱和吸收谱表征了薄膜的形貌、结构、成分和光学性质。实验发现氧气压强对MgZnO薄膜的结构和光学性质有重要影响。当氧气压强由5 Pa增大到45 Pa时,薄膜的PL谱紫外峰蓝移了86meV,表明氧气压强的增大提高了MgZnO薄膜中Mg的溶解度。在15 Pa氧气压强下制备的薄膜显示了独特、均匀的六角纳米柱状结构,其PL谱展示了优异的发光特性,具有比其他制备条件下超强的紫外发射和微弱的可见发光。500~600 nm范围内的绿光发射,我们讨论其机理可能源于深能级中与氧相关的缺陷。使用PLD得到纳米柱状结构表明:优化制备条件,可望使用PLD制备ZnO纳米阵列的外延衬底;可使用PLD技术开发基于ZnO纳米结构的高效发光器件。     

MOCVD生长MgZnO薄膜及太阳盲紫外光电探测器

利用MOCVD在蓝宝石衬底上,通过低温生长实现了立方结构、吸收边在255nm的Mg0.52Zn0.48O合金薄膜,并采用传统湿法刻蚀的方法在薄膜上制备了梳状叉指金电极,构成金属-半导体-金属(MSM)结构,实现了在10V偏压下,器件的光响应峰值在250nm,截止边为273nm的MgZnO太阳盲光电探测器。     

The demonstration of hybrid n-ZnO nanorod/p-polymer heterojunction light emitting diodes on glass substrates

We report a demonstration of heterojunction light emitting diode (LED) based on a hybrid n-ZnO-nanorod/p-polymer layered structure. The ZnO was grown using the aqueous chemical growth (ACG) on top of the polymer(s) which were deposited on glass. The current–voltage (I–V) behavior of the heterojunctions showed good rectifying diode characteristics. Room-temperature electroluminescence (EL) spectra of the LEDs provided a broad emission band over a wide LED color range (430–650 nm), in which both zinc and oxygen vacancy peaks are clearly detected. We present here luminescent devices based on the use of ZnO-nanorods in combination with two different blended and multi-layered p-type polymers. Electroluminescence of the first batch of devices showed that white bluish strong emission for the presently used polymers is clearly observed. We obtained a turn-on voltage of 3 V and break-down voltage equal to −6 V for PVK-TFB blended device. The corresponding values for the NPD-PFO multilayer device were 4 V and −14 V, respectively. The rectification factors were equal to 3 and 10 for the two devices, respectively. The films and devices processed were characterized by scanning electron microscopy (SEM), DEKTAK 3ST Surface Profile, Semiconductor Parameter Analyzer, photoluminescence (PL), and electroluminescence (EL).     

A study of electrical enhancement of polycrystalline MgZnO/ZnO bi-layer thin film transistors dependence on the thickness of ZnO layer

A polycrystalline MgZnO/ZnO bi-layer was deposited by using a RF co-magnetron sputtering method and the MgZnO/ZnO bi-layer TFTs were fabricated on the thermally oxidized silicon substrate. The performances with varying the thickness of ZnO layer were investigated. In this result, the MgZnO/ZnO bi-layer TFTs which the content of Mg is about 2.5 at % have shown the enhancement characteristics of high mobility (6.77–7.56 cm² V⁻¹ s⁻¹) and low sub-threshold swing (0.57–0.69 V decade⁻¹) compare of the ZnO single layer TFT (μ_FE = 5.38 cm² V⁻¹ s⁻¹; S.S. = 0.86 V decade⁻¹). Moreover, in the results of the positive bias stress, the ΔV_on shift (4.8 V) of MgZnO/ZnO bi-layer is the 2 V lower than ZnO single layer TFT (ΔV_on = 6.1 V). It reveals that the stability of the MgZnO/ZnO bi-layer TFT enhanced compared to that of the ZnO single layer TFT.     

不同Ar/O2气压比例条件下立方MgZnO薄膜生长特性及紫外光吸收特性

利用脉冲激光沉积技术在非晶石英衬底上制备了立方结构MgZnO薄膜,研究了在不同Ar/O₂气压比例条件下,立方结构MgZnO薄膜的生长取向、光学带隙和Mg/Zn含量比例的变化规律。当固定氧气分压为2 Pa、通过注入惰性的Ar气使生长气压从2 Pa升高到7 Pa时,MgZnO薄膜的生长取向由（200）向（111）转变。当生长气压从2 Pa升高到6 Pa时,MgZnO薄膜光学带隙变窄。而当生长气压从6 Pa升高到7 Pa时,MgZnO薄膜光学带隙反而变宽。通过XPS数据分析,不同生长气压下MgZnO薄膜光学带隙的变化规律与薄膜Mg/Zn含量比例的变化规律不一致,MgZnO薄膜中Mg和Zn与O的结合情况的变化对薄膜的光学带隙也有影响。