Examination of the effects of high-density plasmas on the surface of HgCdTe

High-density argon-hydrogen plasmas have been demonstrated to be very effective as etchants of CdTe, CdZnTe, and HgCdTe materials for focal plane array applications. Understanding the physical, chemical, and electrical characteristics of these surfaces is critical in elucidating the mechanisms of processing Hg_1−xCd_xTe. The ways in which these plasmas interact with HgCdTe, such as etch rates and loading, have been studied.^1–11 However, little is known on how these plasmas affect the first few atomic layers of HgCdTe. In this study, the effects of high-density plasmas on the surface of HgCdTe were examined. The combination of argon and hydrogen plasma etch leaves a well-ordered, near-stoichiometric surface determined by both x-ray photoelectron spectroscopy and reflection high-energy electron diffraction (RHEED). Starting with Hg_0.78Cd_0.22Te, we were able to produce surfaces with x=0.4 and a RHEED pattern sharp enough to measure 2×1 reconstruction.     

HL-2A托克马克中微波诊断系统

介绍了核聚变装置HL-2A托克马克中各种微波技术在等离子体诊断中的应用。说明了各种诊断的基本原理、电路安排以及在放电中的测量结果。电子回旋辐射(ECE)主要用来测量主等离子体电子温度及其扰动分布。测量的时间分辨率可以达到4m s(扫频)或者1μs(单频),空间分辨率为3 cm。电子温度的测量范围为10 eV~10 kev。微波反射用于等离子体密度分布、等离子体旋转及等离子体密度扰动等方面的测量及研究,在测量密度分布时的时间分辨为1m s,空间分辨大约1 cm左右。微波干涉诊断用来测定偏滤器中等离子体的平均密度变化,时间分辨率为0.1m s。     

Chemical contribution of oxygen to silicon carbide plasma etching kinetics in a distributed electron cyclotron resonance (DECR) reactor

This paper deals with the influence of the oxygen additive on the fluorinated plasma etch rate of silicon carbide. The assumption according to which the oxygen has a direct contribution to silicon carbide etching, by chemical reaction with carbon atoms, is generally reported in the literature. Our etching experiments are performed in a distributed electron cyclotron resonance reactor, on both 3C- and 6H-SiC. An SF₆/O₂ gas mixture (avoiding the presence of C species in the plasma), fluorine saturation conditions and constant ion bombardment energy and flux are used, allowing the study of O₂ contribution exclusively. In these conditions, our results demonstrate the neutrality of O₂ on SiC etching mechanisms. These results will be discussed reinfored both by several other experimental observations.     

Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long-wavelength infrared HgCdTe on Si

We present extended results on the use of a hydrogen plasma to passivate the effects of defects in long-wave ir HgCdTe/Si. Annealed and as-grown epilayers, in situ doped with indium, were exposed to a hydrogen plasma generated in an electron cyclotron resonance (ECR) reactor. Secondary ion mass spectrometry was used to measure the extent of hydrogen incorporation into the epilayers. Hall and photoconductive lifetime measurements were used to assess the efficacy of passivation. The passivation of defects responsible for the scattering and recombination of electrical carriers was observed for most ECR conditions over a range of dislocation densities.     

碲镉系导带电子回旋共振线形分析

用远红外激光磁光光谱实验系统测量了Ｎ型碲镉汞的导带电子回旋共振，记录了远红外激光入射下的高分辨回旋共振线形．计算表明，这些线形的特征及其与一些物理量的关系可用经典的Ｄｒｕｄｅ－模型很好地描述．此外，还用理论与实验拟合的方法获得了载流子弛豫时间τ，并与由弱场低频下迁移率得出的弛豫时间τ作了比较，对两者差别的理论问题作了讨论．     

Dry etching of Hg1−xCdxTe using CH4/H2/Ar/N2 electron cyclotron resonance plasmas

An approach is presented which eliminates the problems caused by hydrocarbon polymer deposition during etching Hg_1-x Cd_xTe with CH₄/H₂ based plasmas. We find that the addition of N₂ to the plasma inhibits polymer deposition in the chamber and on the sample. We speculate that atomic nitrogen formed from N₂ in the plasma has several beneficial effects: the elimination of polymer precursors, the reduction of the atomic hydrogen concentration, and a potential increase of methyl radical concentration. Evidence for the reaction between the nitrogen and the polymer precursors is presented. It is also demonstrated that the addition of N₂ to CH₄/H₂ based electron cyclotron resonance (ECR) plasmas used to etch HgCdTe eliminates the roughness normally formed during etching and results in a steadier etch rate.     

On the heating mechanism of electron cyclotron resonance thruster immerged in a non-uniform magnetic field

To study the heating mechanism of electron cyclotron resonance thruster(ECRT) immersed in a non-uniform magnetic field, experiments and simulations are performed based on an electron cyclotron resonance plasma source at ASIPP. It is found that the first harmonic of electron cyclotron resonance is essential for plasma ignition at high magnetic field(0.0875 T), while the plasma can sustain without the first and second harmonics of electron cyclotron resonance at low magnetic field(till 0.0170 T). Evidence of radial hollow density profile indicates that upper hybrid resonance, which has strong edge heating effect, is the heating mechanism of low-field ECRT. The heating mode transition from electron cyclotron resonance to upper hybrid resonance is also revealed. Interestingly, the evolutions of electron temperature and electron density with input power experience a ‘delayed' jump, which may be correlated with the different power levels required for cyclotron and ionization. Moreover, when the field strength decreased, the variation of electron density behaves in an opposite trend with that of electron temperature,implying a possible competition of power deposition between them. The present work is of great interest for understanding the plasma discharge in ECRT especially immersed in a non-uniform magnetic field, and designing efficient ECRT using low magnetic field for economic space applications.     

Cyclotron production of the Ag, Pd, Rh radionuclides by Pd(p,x) nuclear processes

Production cross-sections of the ^105g+m,106mAg, ^100,101Pd, and ^{100g+m,101m,105g+m}Rh radionuclides through proton-induced reactions on natural palladium were measured up to 40 MeV by using a stacked-foil activation technique combined with high-resolution γ-ray spectrometry. The production cross-sections of ¹⁰¹Pd and ^{100g+m,105g+m}Rh radionuclides have been reported here for the first time from the ^natPd(p,x) nuclear processes. The present results are compared with the available literature values as well as the theoretical data calculated by the TALYS and the ALICE-IPPE computer codes. A quantitative comparison of the present results with the theoretical data has also been done with several deviation factor definitions. Optimal production pathways of the therapeutic ^105gRh radionuclide with minimal contamination using cyclotrons are discussed elaborately.