Photoassisted growth and nitrogen doping of ZnSe

ZnSe was grown on GaAs(100) substrates by photoassisted MOVPE using the precursors dimethylzinc-triethylamine (DMZn-TEN) and ditertiarybutylselenide (DtBSe). The optimal growth temperature was T_g = 300°C. Above 300°C no enhancement of growth rate was observed under illumination. Furthermore, nitrogen doping experiments were performed using phenylhydrazine, allylamine and tert-butylamine as nitrogen precursors. Nitrogen concentrations up to 10¹⁹ cm⁻³ (SIMS) were achieved with input flow ratios as low as [PhHz]/[Se] = 4 × 10⁻⁴. All as-grown samples were highly compensated. Successful nitrogen incorporation was also observed with allylamine. However, the use of tert-butylamine together with the adduct compound DMZn-TEN showed no incorporation of nitrogen.     

Growth and annealing effect of high-quality ZnSe:N/ZnSe by MOCVD

The ZnSe : N epitaxial layers were grown on (1 1 0) ZnSe substrates in a low-pressure metalorganic chemical vapor deposition (MOCVD) system using hydrogen as a carrier gas, and using ammonia as a dopant source. In order to obtain highly doped ZnSe : N epitaxial layers, the optimum growth and doping conditions were determined by studying the photoluminescence (PL) spectra from the ZnSe epitaxial layers grown at different ammonia flux and VI/II flux ratio. Furthermore, in order to enhance the concentration of active nitrogen in ZnSe epitaxial layer, a rapid thermal anneal technique was used for post-heat-treating. The results show that the annealing temperature of over 1023 K is necessary. Beside, a novel treatment method to obtain a smooth substrate surface for growing high quality ZnSe epitaxial layers is also described.     

Diode characteristics of Li3N-diffused ZnSe grown by MOVPE

We have fabricated a ZnSe diode using Li₃N diffusion technique for the purpose of forming p-type ZnSe. The maximum hole concentration in the Li₃N-diffused ZnSe layer, which has been grown on a GaAs substrate by metalorganic vapor phase epitaxy, was as high as 10¹⁸ cm⁻³. The ohmic contact to the p-type ZnSe has been demonstrated and the specific contact resistance of Au/p-ZnSe was 1 × 10⁻² Ω · cm². The Li₃N diffusion technique is useful for the bfabrication of ohmic contacts to p-ZnSe.     

Synthesis and properties of zinc-nitrogen compounds for the MOVPE of p-type ZnSe

Novel nitrogen-based compounds for p-type doping of ZnSe have been studied. Photoluminescence spectra of epilayers doped with synthesized zinc amides Zn(NRR')₂ and with corresponding amines HNRR' (R and R' are organic ligands) indicate an insufficient stability of the Zn---N bond preventing effective doping of the tested zinc amides. Doping efficiency is improved by replacing t-butyl groups (---CMe₃) of the ligands by trimethylsilyl groups (---SiMe₃). Nitrogen incorporation under usual growth conditions remained, however, too low for device applications.     

Metalorganic chemical vapor epitaxy and doping of ZnMgSSe heterostructures for blue emitting devices

Blue-green semiconductor laser diodes operating at room temperature are still the domain of wide bandgap II–VI compound semiconductors. CW operation at room temperature and hours of lifetime were reported. However, the conductivity control, defect generation and the ohmic contacts still need improvement. Therefore we focused our work on the MOVPE growth and the optimization of ZnMgSSe/ZnSSe/ZnSe heterostructures as well as on nitrogen doping of ZnSe. To verify the layer quality characterization was carried out by X-ray diffraction, electron probe microanalysis, electrical measurements and photoluminescence. ZnMgSSe/ZnSSe/ZnSe and ZnSSe/ZnSe quantum wells and superlattices were grown to investigate structural as well as interface properties. Electron beam and optical pumping was used to clarify the laser mechanism and to clarify the suitability of a MOVPE process to grow laser quality material. The electrical compensation of ZnSe doped with nitrogen is still controversially discussed whereas high n-type doping with chlorine was reproducible achieved. ZnSe: N doped at different growth conditions (II/VI ratio, growth temperature, nitrogen supply) using N₂ excited in a plasma source or by the use of nitrogen containing precursors was investigated to study the compensation mechanisms.     

Optical properties of hydrogenated amorphous silicon films doped with fluorinated gases

Doped amorphous silicon films were prepared by plasma-enhanced chemical vapour deposition of silane and hydrogen mixtures, using phosphorus pentafluoride (PF₅) and boron trifluoride (BF₃) as dopant precursors. The films were studied by UV-vis spectroscopy and their photo and dark conductivity were measured, the latter as a function of temperature. The optical gap of the n-type samples, doped with PF₅, diminished as the concentration of this gas in the plasma was increased. However, the optical gap of p-type samples, doped with BF₃, did not show any appreciable optical gap decrease as the concentration of BF₃ was varied from 0.04% to 4.7%. The dark conductivity of the p-type films at these extremes of the doping range were 7.6 × 10⁻¹⁰ and 3.5 × 10⁻¹ Ω⁻¹ cm⁻¹, respectively.     

CBE growth of high-quality AlGaAs/GaAs heterostructures for HEMT applications

AlGaAs/GaAs heterostructures were grown by chemical beam epitaxy using triethylgallium, triisobutylaluminium and pure arsine in flow control mode with hydrogen as carrier gas. For substrate temperatures of 580°C and V/III ratios of 10, high quality AlGaAs layers are obtained; heterostructures show abrupt and smooth interfaces. Modulation doping with silicon evaporated from a conventional effusion cell gives two-dimensional electron gases with carrier densities up to 1×10¹² cm^-2. Mobilities of 70000 cm²/V·s are obtained at 77 K for carrier densities of 4×10¹¹ cm^-2. The lateral homogeneity of the heterostructures in layer thickness, composition and doping level is excellent. Perfect morphology with defect densities of about 100 cm^-2 is observed. High electron mobility transistors (gate length 0.3 nm) fabricated from quantum well structures show a transconductance of about 380 mS/mm.     

High-quality InP grown by chemical beam epitaxy

InP films were grown by chemical beam epitaxy using trimethylindium (TMI) and pure phosphine (PH₃) in a flow control mode with hydrogen as the carrier gas, with the TMI flow rate fixed at 3 SCCM. Substrate temperatures were varied between 505 and 580°C and V/III ratios from 3 to 9. InP layers with high optical quality (intense and narrow excitonic transition lines) and high crystalline quality (narrow and symmetric X-ray diffraction peaks) could be grown only within a narrow parameter window around a substrate temperature of 545°C (δT_s ≤ 25°C) and a V/III ratio of 5.5 (δ(V/III) ≤ 2). Carrier densities of 8 × 10¹⁴ cm^-3 with mobilities of 70000 cm²/V.s measured at 77 K were obtained for growth conditions close to the edge of this parameter window towards low V/III ratios. The growth rate of inP was also clearly at its maximum in the given parameter window. Leaving the window, by changing either the growth temperature or the V/III ratio, significantly decreased the growth rate. This reduced growth rate was accompanied by a degradation in the crystalline quality. We also demonstrate that for higher TMI flow the parameter window shifts to higher growth temperatures. The InP could be doped effectively with Si in the range from 9 × 10¹⁵ to 3 × 10¹⁸ cm^-3.     

双温区热扩散掺杂Fe2+∶ZnSe激光晶体的制备及激光输出性能

本文以CVD ZnSe晶片为基质材料,以FeSe粉末为掺杂物,采用双温区热扩散掺杂技术获得了尺寸为Ø22 mm×4 mm的Fe²⁺∶ZnSe激光晶体。通过二次离子质谱(SIMS)测试该晶体样品表面铁离子浓度为3.43×10¹⁸ cm^-3,并通过X射线光电子能谱(XPS)分析了晶体样品中铁元素的离子价态。采用UV/Vis/NIR分光光度计和傅里叶红外光谱仪测试了Fe²⁺∶ZnSe激光晶体的透过谱图。测试结果显示,在3.0 μm处出现了明显的Fe²⁺吸收峰,峰值透过率为5.5%。以波长为2.93 μm的Cr, Er∶YAG激光器为泵浦源,温度77 K时抽运尺寸10 mm×10 mm×4 mm的 Fe²⁺∶ZnSe晶体,获得了能量为191 mJ、中心波长4.04 μm的中红外激光输出,光光转换效率13.84%。     

Identification of gaseous oxygen and nitrogen in bubble inclusions in Bi4(GeO4)3 (BGO) crystals by means of Raman spectroscopy

Bubble inclusions in BGO crystals have been studied by means of Raman spectoscopy. Since the crystals were grown under ambient atmospheric conditions, we focused our attention on oxygen and nitrogen. Both species are diatomic homonuclear molecules which are vibrationally Raman active. Concerning the vibrational part of the O₂ and N₂ Raman spectra, no evidence was found for the presence of both gases. However, in the spectrum below the lowest 64 cm^-1 energy mode of BGO three faint peaks were found which show the characteristic features of the rotational spectra of O₂ and N₂. It was found that the composition of the inclusion atmosphere was enriched by oxygen compared to the composition of the air.     

Growth of 1.55 μm DH laserstructures using TBAs and TBP in MOMBE

In a comparative study we have chosen TBAs and TBP as well as AsH₃ and PH₃ for the growth of InP/GaInAs(P) heterostructures for laser applications in a production metalorganic molecular beam epitaxy (MOMBE) system. The n-type doping was performed with Si from an effusion cell, whereas for the p-type doping Be and DEZn were utilized. InP layers using TBP under optimized cracking conditions exhibit excellent surface morphology with good electrical properties in the low 10¹⁵ cm⁻³ range of carrier concentrations. The MOMBE growth mechanism is not disturbed by the hydride replacement compound. This allows for a convenient replacement without losing calibration data from the hydride process. Broad-area DH laserstructures with GaInAsP (λ = 1.55 μm) active regions were grown with AsH₃/PH₃ and TBAs/TBP. Comparable threshold current densities in the range of 1.6-2.3 kA/cm² are achieved for the lasers, grown with both sets of precursors combined with DEZn source doping. These results are in good agreement with the standard set by the hydride MOVPE process.     

The role of hydrogen in low-temperature MOVPE growth and carbon doping of In0.53Ga0.47As for InP-based HBT

Hydrogen radicals are decisive for the low-temperature growth and carbon doping of In_0.53Ga_0.47As in LP-MOVPE. This is demonstrated for the growth of highly p-type doped In_0.53Ga_0.47As layers with CCl₄ as dopant source. Perturbed angular correlation measurements (PAC) were used to investigate the passivation of acceptors by hydrogen in low-temperature grown In_0.53Ga_0.47As. Based on the above analysis an InP-based layer stack is developed which employs low-temperature growth of the base layer, high-temperature growth of the remaining HBT layers, and an in situ post-growth annealing under TMAs/N₂ ambient.     

Heavily carbon-doped p-type InGaAs by MOMBE

Carbon-doped In_xGa_1−xAs layers (x=0−0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As₄) and solid indium (In) as sources of Ga, As and In, respectively. The carrier concentration is strongly affected by growth temperature and indium beam flux. Heavy p-type doping is obtained for smaller In compositions. The hole concentration decreases with the indium composition from 0 to 0.8, and then the conductivity type changes from p to n at x=0.8. Hole concentrations of 1.0×10¹⁹ and 1.2×10¹⁸ cm^-3 are obtained for x=0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped In_xGa_1−xAs by MBE. Preliminary results on carbon-doped GaAs/In_xGa_1−xAs strained layer superlattices are also discussed.     

高质量硼掺杂单晶金刚石同质外延及电学性质研究

突破高质量、高效金刚石掺杂技术是实现高性能金刚石功率电子器件的前提。本文利用微波等离子体化学气相沉积(MPCVD)法,以三甲基硼为掺杂源,制备出表面粗糙度0.35 nm,XRD(004)摇摆曲线半峰全宽28.4 arcsec,拉曼光谱半峰全宽3.05 cm^-1的高质量硼掺杂单晶金刚石。通过改变气体组分中硼元素的含量,实现了10¹⁶~10²⁰ cm^-3的p型金刚石可控掺杂工艺。随后,研究了硼碳比、生长温度、甲烷浓度等工艺条件对p型金刚石电学特性的影响,结果表明:在硼碳比20×10^-6、生长温度1 100 ℃、甲烷浓度8%、腔压160 mbar(1 mbar=100 Pa)时p型金刚石迁移率达到207 cm²/(V·s)。通过加氧生长可以提升硼掺杂金刚石结晶质量,降低杂质散射。当氧气浓度为0.8%时,样品空穴迁移率提升至 614 cm²/(V·s)。     

4d- and 5d-transition metal acceptor doping of InP

We present a detailed study of the electrical activation of the 4d- and 5d-transition metals Ru, Rh, Os and Ir in InP. The layers investigated were grown by metalorganic chemical vapor deposition and investigated by secondary ion mass spectroscopy and deep level transient spectroscopy. We show that InP doping with these transition metals is possible up to concentrations above 10¹⁸ cm⁻³ without any formation of macroscopic precipitates. All of these transition metals offer a low diffusivity and induce deep levels in InP. Deep levels close to the middle of the bandgap are observed for Rh and Ru doping, making them interesting candidates to turn InP semi-insulating. The transition-metal-related deep level concentrations achieved so far are well above 10¹⁵ cm⁻³. The electrically active concentration of these transition metals is strongly dependent on their particular reactivity, especially with hydrogen, and ranges between 0.1% for Rh and 5% for Os. In the case of Rh doping the electrically active concentration can be enhanced by a factor of 5 using nitrogen carrier gas instead of hydrogen.     

The stability and surface reactivity of gallium phosphide nanocrystals

The stability and surface reactivity of Gal? nanocrystals were characterized by TG-DTA, XRD and XPS measurements. The samples were heated in O₂ and N₂ atmospheres respectively. The experimental curve which describes the mass change as a function of temperature shows that the mass decreases under 330°C but increases in two stages between 33°C and 550°C. The curves obtained in O₂ and N₂ are obviously different. The results of XPS indicate that the density of oxygen atoms bonded chemically to the gallium atoms on the surface increases when the sample is heated in O₂ up to 200°C, whereas the density of nitrogen atoms increased when heated to 330°C in N₂. It can be concluded that the N₂ could be activated on the surface of GaP nanocrystals at a rather low temperature, and highly reactive nitrogen atoms formed. Our result obtained makes it possible to synthesize a series of nitrogen-containing compounds in N₂ gas under moderate conditions.     

The growth of Si/SiGe/Si structures for heterojunction bipolar transistor by gas source molecular beam epitaxy

Three n–p–n Si/SiGe/Si heterostructures with different layer thickness and doping concentration have been grown by a home-made gas source molecular-beam epitaxy (GSMBE) system using phosphine (PH₃) and diborane (B₂H₆) as n-and p-type in situ doping sources, respectively. Heterojunction bipolar transistors (HBTs) have been fabricated using these structures and a current gain of 40 at 300 K and 62 at 77 K have been obtained. The influence of thickness and doping concentration of the deposited layers on the current gain of the HBTs is discussed.     

单层n型MoS2/p型c-Si异质结太阳电池数值模拟

单层二硫化钼(MoS₂)是一种具有优异光电性能的半导体材料,在太阳能能量转换中表现出很大的应用潜力。本文基于AMPS模拟软件,对单层n型MoS₂/p型c-Si异质结太阳电池进行了数值模拟与分析。通过模拟优化,n型MoS₂的电子亲和能为3.75 eV、掺杂浓度为10¹⁸ cm^-3,p型c-Si的掺杂浓度为10¹⁷ cm^-3时,太阳电池能够取得最高22.1%的转换效率。最后模拟了n型MoS₂/p型c-Si异质结界面处的界面态对太阳电池性能的影响,发现界面态密度超过10¹¹ cm^-2·eV^-1时会严重影响太阳电池的光伏性能。     

Radical-assisted metalorganic chemical vapor deposition of ZnSe

Radical-assisted metalorganic chemical vapor deposition (MOCVD) of ZnSe has been performed by using diethylzinc (DEZn) and diethylselenide (DESe) as a source and azo-t-butane ((t-C₄H₉)₂N₂)and nitrogen trifluoride (NF₃) as co-reactants. The growth rate was significantly increased in the measured temperature range of 623 to 723 K.     

Boron-doped a-SiOx:H films prepared by photo-CVD technique

The optoelectronic and structural properties of p-type a-SiO_x:H films have been studied. The deposition parameters e.g. chamber pressure and diborane to silane ratio are optimized to get a film with dark conductivity (σ_d) 7.9×10⁻⁶ S cm⁻¹ and photoconductivity 9.3×10⁻⁶ S cm⁻¹ for an optical gap (E₀₄) of 1.94 eV. The decrease of optical gap accompanied by the increase of conductivity is due to less oxygen incorporation in the film, which is substantiated by the decrease of the intensity of SiO absorption spectra. The properties are very much effected by the chamber pressure and diborane to silane ratio.