Cd饱和气氛退火对碲锌镉晶体导电类型转变界面的影响

在富Te生长条件下,通过垂直布里奇曼法制备的部分碲锌镉晶体内存在导电类型转变界面。采用富Te液相外延技术在含有导电类型转变界面的碲锌镉衬底上生长碲镉汞薄膜,制成的红外焦平面探测器响应图上存在明显的响应不均匀分界面。碲锌镉晶体的导电类型转变由缺陷类型的不同引起,为消除碲锌镉衬底的导电类型转变界面,提升碲镉汞红外焦平面的成像质量,对含有导电类型转变界面的碲锌镉晶体进行了Cd饱和气氛退火实验,研究了时间和温度等退火条件对晶体导电类型转变界面的影响,探讨了Cd间隙和Cd空位缺陷的形成机制,为晶体生长过程中的Cd空位缺陷抑制提出了解决思路。     

原位退火对碲锌镉晶体第二相夹杂缺陷的影响

采用传统布里奇曼法生长碲锌镉晶体,在配料过程中添加适当过量的Cd,并在晶体生长结束阶段的降温过程中加入晶锭原位退火工艺,晶体的第二相夹杂缺陷得到了有效抑制。根据晶体第二相夹杂缺陷的形成机理,结合热扩散理论和碲锌镉晶体的P-T相图,研究了退火温度对晶体第二相夹杂缺陷密度和粒度（尺寸）的影响,获得了抑制碲锌镉晶体第二相夹杂缺陷的退火条件。利用优化的退火条件制备碲锌镉晶体,晶体第二相夹杂缺陷的尺寸小于10 μm,密度小于250 cm－2。     

碲硒锌镉单晶体的垂直布里奇曼法生长与性能研究

碲锌镉(CdZnTe)是目前最重要的室温半导体核辐射探测器材料。而在CdZnTe晶格中以Se替位部分Te得到碲硒锌镉(CdZnTeSe),将使得晶格中离子键的成分增加,从而提高晶体的硬度,降低Cd空位和Te夹杂物缺陷浓度,提升材料质量。为了获得适宜于核辐射探测器制备的CdZnTeSe晶体,研究了富Te条件下CdZnTeSe晶体的垂直布里奇曼法生长,成功制备出直径为21 mm、长度超过70 mm的Cd_0.9Zn_0.1Te_0.97Se_0.03单晶锭。所得Cd_0.9Zn_0.1Te_0.97Se_0.03晶体的(110)面X射线衍射摇摆半峰宽达到0.104°,而Te夹杂相的尺寸小于5μm,表明晶体具有良好结晶性。Cd_0.9Zn_0.1Te_0.97Se_0.03晶锭尾部的能带隙和红外透过率均低于晶锭的头部和中部,这可归因于Cd_0.9<...     

碲锌镉晶片中位错与Te沉淀的透射电子显微分析

采用透射电子显微镜对碲锌镉晶体材料的缺陷特性进行了分析,观察并研究了碲锌镉晶体中Te沉淀相形貌和Te沉淀周围的棱柱位错环.认为棱柱位错的形成是由Te沉淀相的析出引起的,而沉淀相在基体中的析出与基体形成错配应力,又造成位错的增殖.Te沉淀与棱柱位错两种缺陷是相互依存的.     

碲锌镉晶片中位错与Te沉淀的透射电子显微分析

采用透射电子显微镜对碲锌镉晶体材料的缺陷特性进行了分析，观察并研究了碲锌镉晶体中Te沉淀相形貌和Te沉淀周围的棱柱位错环. 认为棱柱位错的形成是由Te沉淀相的析出引起的，而沉淀相在基体中的析出与基体形成错配应力，又造成位错的增殖. Te沉淀与棱柱位错两种缺陷是相互依存的.     

碲锌镉晶体第二相夹杂物特性研究

高质量的碲锌镉单晶是制备碲镉汞红外焦平面器件的理想衬底材料,然而目前碲锌镉材料中的第二相夹杂物严重制约着晶体的质量.根据红外透射形貌的描述和表征,碲锌镉晶体的常见夹杂物被分成了五类,并在此基础上讨论了各自的形成机制,A、B和C类夹杂物与化学配比及其变化密切相关,而D和E类夹杂物与源材料中或者在生长工艺控制过程中氧含量相关.进一步的研究表明大尺寸、高密度的Te夹杂物将会严重降低红外透过率,同时腐蚀坑密集分布在与Cd夹杂对应的六重对称线上,该结果揭示了第二相夹杂物会产生其他缺陷的增殖,但夹杂物引起的应力影响区域是局限的.     

改进的垂直布里奇曼法生长CdZnTe晶体中的成分偏离现象

采用多种测试方法,对改进的垂直布里奇曼法生长Cd0.96Zn0.04Te晶体中的成分偏离标准化学计量比现象及其对晶体性能的影响进行了研究.X射线能谱成分测试表明,在晶锭的头部即初始结晶位置,(Cd Zn)/Te比大于1;而在中部及末端,小于1.表明这种方法生长的CZT晶体仍然存在对标准化学计量比的偏离现象,开始结晶是在富Cd熔体中,生长至中后段则是在富Te条件下进行的.PL谱测试表明,富Cd的晶片内存在大量Te空位,严重富Te的晶片内Cd空位及其杂质复合体等引起的缺陷密度显著增加.晶体红外透过率测试结果表明,接近化学计量配比的CZT晶片具有高的红外透过率.     

改进的垂直布里奇曼法生长CdZnTe晶体中的成分偏离现象

采用多种测试方法,对改进的垂直布里奇曼法生长Cd0.96Zn0.04Te晶体中的成分偏离标准化学计量比现象及其对晶体性能的影响进行了研究.X射线能谱成分测试表明,在晶锭的头部即初始结晶位置,(Cd+Zn)/Te比大于1;而在中部及末端,小于1.表明这种方法生长的CZT晶体仍然存在对标准化学计量比的偏离现象,开始结晶是在富Cd熔体中,生长至中后段则是在富Te条件下进行的.PL谱测试表明,富Cd的晶片内存在大量Te空位,严重富Te的晶片内Cd空位及其杂质复合体等引起的缺陷密度显著增加.晶体红外透过率测试结果表明,接近化学计量配比的CZT晶片具有高的红外透过率.     

50 mm×50 mm高性能HgCdTe液相外延材料的批生产技术

采用富碲垂直液相外延技术实现了50 mm×50 mm×3高性能碲镉汞外延材料的制备.外延工艺的样品架采用了三角柱体结构,并设计了防衬底背面粘液的样品夹具.为保证大面积材料的均匀性,工艺中加强了对母液温度均匀性和组分均匀性的控制,50 mm×50 mm外延材料的组分均方差达到了0.000 4,厚度均方差达到了0.4μm.在批量生产技术中,加强了对单轮次生长环境的均匀性和生长轮次之间生长条件一致性的控制,同一轮次生长的3片材料之间的组分偏差小于0.000 4,厚度偏差小于0.1μm,不同生长轮次之间材料的组分之间的波动在±0.002左右,厚度之间的波动在±2μm左右.工艺中对碲锌镉衬底的Zn组分、缺陷尺寸和缺陷密度也加强了控制,以控制大面积外延材料的缺陷,晶体双晶衍射半峰宽(FWHM)小于30弧秒,外延材料的位错密度小于1×105cm~(-2),表面缺陷密度小于5 cm~(-2).外延材料经过热处理后,汞空位型的P型Hg0.78Cd0.22Te外延材料77 K温度下的载流子浓度被控制在8~20×1015cm-3,空穴迁移率大于600 cm2/Vs.材料整体性能和批生产能力已能满足大规模碲镉汞红外焦平面探测器的研制需求.     

分子束外延HgCdTe/CdZnTe(211)B表面缺陷研究

HgCdTe材料的表面缺陷是造成探测器性能下降的主要原因之一。采用聚焦离子束（Focused Ion Beam, FIB）、扫描电子显微镜（Scanning Electron Microscope, SEM）和能量色散X射线光谱仪（Energy Dispersive X-ray Spectrometer, EDX）研究了碲锌镉（CdZnTe)基HgCdTe外延层的表面缺陷。通过分析不同类型缺陷形成的原因,确定缺陷起源于HgCdTe材料生长过程。缺陷的形状与生长条件关系密切。凹坑及火山口状缺陷与Hg缺乏/稍高生长温度、分子束源坩埚中材料形状变化造成的不稳定束流有关。金刚石状缺陷和火山口状/金刚石状复合缺陷的产生与Hg/Te高束流比、低生长温度相关。在5 cm×5 cm大小的CdZnTe(211)B衬底表面上生长出了组分为0.216、厚度约为6.06~7 μm的高质量HgCdTe外延层。同时还建立了缺陷类型与HgCdTe薄膜生长工艺的关系。该研究对于制备高质量HgCdTe/CdZnTe外延层具有参考意义。     

Heterojunction blocking contacts in MOCVD grown Hg1-xCdxTe long wavelength infrared photoconductors

The theoretical and experimental performance of Hg_1-xCd _xTe long wavelength infrared (LWIR) photoconductors fabricated on two-layer heterostructures grown by in situ MOCVD has been studied. It is shown that heterojunction blocking contact (HBC) photoconductors, consisting of wider bandgap Hg_1-xCd_x Te on an LWIR absorbing layer, give improved responsivity, particularly at higher applied bias, when compared with two-layer photoconductors incorporating n⁺/n contacts. An extension to existing device models is presented, which takes into account the recombination rate at the heterointerface and separates it from that occurring at both the contact-metal/semiconductor and passivant/semiconductor interfaces. The model requires a numerical solution to the continuity equation, and allows the device responsivity to be calculated as a function of applied electric field. Model predictions indicate that a change in bandgap across the heterointerface corresponding to a compositional change of Δx⩾0.04 essentially eliminates the onset of responsivity saturation due to minority carrier sweepout at high applied bias. Experimental results are presented for frontside-illuminated n-type Hg_1-xCd_xTe photoconductive detectors with either n⁺/n contacts or heterojunction blocking contacts. The devices are fabricated on a two-layer in situ grown MOCVD Hg_1-xCd_xTe wafer with a capping layer of x=0.31 and an LWIR absorbing layer of x=0.22. The experimental data clearly demonstrates the difficulty of forming n ⁺/n blocking contacts on LWIR material, and indicates that heterojunctions are the only viable technology for forming effective blocking contacts to narrow bandgap semiconductors     

Investigation of broad-band quantum-well infrared photodetectorsfor 8-14-μm detection

Typical quantum-well infrared photodetectors (QWIPs) exhibit a rather narrow spectral bandwidth of 1-2 μm. For certain applications, such as spectroscopy, sensing a broader range of infrared radiation is highly desirable. In this paper, we report the design of four broad-band QWIPs (BB-QWIPs) sensitive over the 8-14-μm spectral range. Two n-type BB-QWIPs, consisting of three and four quantum wells of different thickness and/or composition in a unit cell which is then repeated 20 times to create the BB-QWIP structure, are demonstrated. The three-well n-type In_xGa_1-xAs-Al_yGa_1-yAs BB-QWIP was designed to have a response peak at 10 μm, with a full-width at half-maximum (FWHM) bandwidth that varies with the applied bias. A maximum bandwidth of Δλ/λ_p=21% was obtained for this device at V_b=-2 V. The four-well n-type In_xGa_1-xAs-GaAs BB-QWIP not only exhibits a large responsivity of 2.31 A/W at 10.3 μm and V_b=+4.5 V, but also achieves a bandwidth of Δλ/λ_p=29% that is broader than the three-well device. In addition, two p-type In _xGa_1-xAs-GaAs BB-QWIPs with variable well thickness and composition, sensitive in the 7-14-μm spectral range, are also demonstrated. The variable composition p-type BB-QWIP has a large FWHM bandwidth of Δλ/λ_p=48% at T=40 K and V_b=-1.5 V. The variable thickness p-type BB-QWIP was found to have an even broader FWHM bandwidth of Δλ/λ _p=63% at T=40 K and V_b=1.1 V, with a corresponding peak responsivity of 25 mA/W at 10.2 μm. The results show that a broader and flatter spectral bandwidth was obtained in both p-type BB-QWIP's than in the n-type BS-QWIP's under similar operating conditions     

Si/Si1-xGex heterojunction bipolartransistors produced by limited reaction processing

Si/Si_1-xGe_x heterojunction transistors (HBTs) fabricated by a chemical vapor deposition (CVD) technique are reported. A rapid thermal CVD limited-reaction processing (LRP) technique was used for the in situ growth of all three device layers, including a 20-mm Si_1-xGe_x layer in the base. The highest current gains observed (β=400) were for a Si/Si_1-x Ge_x HBT with a base doping of 7×10¹⁸ cm^-3 near the junction and a shallow arsenic implant to form ohmic contacts and increase current gain. Ideal base currents were observed for over six decades of current and the collector current remained ideal for nearly nine current decades starting at 1 pA. The bandgap difference between a p-type Si layer doped to 5×10¹⁷ cm^-3 and the Si_1-xGe_x(x=0.31) base measured 0.27 eV. This value was deduced from the measurements of the temperature dependence of the base current and is in good agreement with published calculations for strained Si_1-xGe_x layers on Si     

Hg0.4Cd0.6Te 1.55-μm avalanche photodiodenoise analysis in the vicinity of resonant impact ionization connectedwith the spin-orbit split-off band

The authors describe the electrical and optical characterization of three Hg_1-xCd_xTe avalanche photodiodes manufactured using planar technology with composition parameter x near 0.6. This alloy composition leads to devices that are well suited for 1.55-μm detection. From the noise analysis under multiplication, the authors show the tight dependence of the ratio β/α (of the hole; and electron ionization coefficient, respectively) upon x and the ratio Δ/E_g where Δ is the spin-orbit splitting energy and E _g is the bandgap energy. It turns out that in these alloys around x=0.6, Δ is very close to the bandgap energy so β/α reaches its maximum value. Owing to this property, which is characteristic of II-VI compounds, Hg_1-xCd_xTe is a good candidate for 1.3-μm to 1.6-μm avalanche photodiodes     

High-density photogenerated free-carrier spin relaxation processesin Wurtzite semiconductors: CdSe and semimagnetic semiconductorCd1-xMnxSe

Picosecond time-resolves spin relaxation kinetics of high-density free carriers is investigated at low temperatures on CdSe (x=0) and in the dilute semimagnetic semiconductor Cd_1-xMn_x Se for x=0.05 and 0.10. The fast spins relaxation observed in CdSe results from a mechanism associated with the noncentrosymmetric character of the band structure for this material. This process is similar to the one proposed by M.I. D'yakonov and V.I. Perel' (1971) for the zinc blende crystal structures. The spin relaxation times in CdSe are on the order of 30 ps. The spin relaxation time are <20 ps in semimagnetic semiconductor Cd_1-xMnSe and are consistent with spin-flip Raman scattering measurements. The increase in spin relaxation rate relative to CdSe is explained in terms of the carrier spin exchange between the carriers and the magnetic spin sites. A probable cause for the reduction in the observed spin polarization factor for carriers in Cd_1-xMn_xSe ( x≠0) is presented     

Electrical properties of heavily doped polycrystallinesilicon-germanium films

The electrical properties of polycrystalline silicon-germanium (poly-Si_1-xGe_x) films with germanium mole fractions up to 0.56 doped by high-dose ion implantation are presented. The resistivity of heavily doped p-type (P⁺) poly-Si_1-x Ge_x is much lower than that of comparably doped poly-Si, because higher levels of boron activation and higher hole mobilities are achieved in poly-Si_1-xGe_x. The resistivity of heavily doped n-type (N⁺) poly-S_1-xGe_x is similar to that of comparably doped poly-Si for x<0.45; however, it is considerably higher for larger Ge mole fractions due to significant reductions in phosphorus activation. Lower temperatures (~500°C), as well as lower implant doses, are sufficient to achieve low resistivities in boron-implanted poly-Si_1-xGe_x films, compared to poly-Si films. The work function of P⁺ poly-Si_1-xGe_x decreases significantly (by up to ~0.4 Volts), whereas the work function of N⁺ poly-Si_1-xGe_x decreases only slightly, as Ge content is increased. Estimates of the energy bandgap of poly-Si_1-xGe_x show a reduction (relative to the bandgap of poly-Si) similar to that observed for unstrained single-crystalline Si_1-xGe_x for a 26% Ge film, and a reduction closer to that observed for strained single-crystalline Si _1-xGe_x for a 56% Ge film. The electrical properties of poly-Si_1-xGe_x make it a potentially favorable alternative to poly-Si for P⁺ gate-material applications in metal-oxide-semiconductor technologies and also for p-channel thin-film transistor applications     

Si/Si1-x-yGexCy/Si heterojunctionbipolar transistors

We report the first Si/Si_1-x-yGe_xC_y /Si n-p-n heterojunction bipolar transistors and the first electrical bandgap measurements of strained Si_1-x-yGe_x C_y on Si (100) substrates. The carbon compositions were measured by the shift between the Si_1-x-yGe_xC_y and Si_1-xGe_x X-ray diffraction peaks. The temperature dependence of the HBT collector current demonstrates that carbon causes a shift in bandgap of +26 meV/%C for germanium fractions of x=0.2 and x=0.25. These results show that carbon reduces the strain in Si_1-x Ge_x at a faster rate than it increases the bandgap (compared to reducing x in Si_1-xGe_x), so that a Si _1-x-yGe_xC_y film will have less strain than a Si_1-xGe_x film with the same bandgap     

Theory of optical nutation in direct-gap semiconductors due toultrashort resonant laser irradiation

An analytical investigation of optical nutation in direct-gap semiconductors such as GaAs, InSb, and Hg_1-xCd_xTe based on the time-dependent perturbation technique is discussed. The crystals are considered to be irradiated by short pulsed moderate power near-resonant lasers producing significant density of optically-induced free electron-hole pairs. Incoherent dephasing mechanisms have been introduced phenomenologically into the coherent radiation-semiconductor interaction model. The theory, on application to the case of a specific crystal such as Hg_1-xCd_xTe with x=0.18 irradiated by a pulsed 10.6 μm CO₂ laser, manifests distinctly the occurrence of ringing behavior in the transmitted intensity, transient dispersion, and absorption even in the absence of any theoretical averaging or the consideration of the effective density of states     

Work Function Tunability of Refractory Metal Nitrides by Lanthanum or Aluminum Doping for Advanced CMOS Devices

A lanthanum (La)-doped HfN is investigated as an n-type metal gate electrode on SiO₂ with tunable work function. The variation of La concentration in (HfinfinLa_1-x)N_y modulates the gate work function from 4.6 to 3.9 eV and remains stable after high-temperature annealing (900degC to 1000degC), which makes it suitable for n-channel MOSFET application. An ultrathin high-fc dielectric layer was formed at the metal/SiO₂ interface due to the (HfinfinLa_1-x)N_y and SiO₂ interaction during annealing. This causes a slight reduction in the effective oxide thickness and improves the tunneling current of the gate dielectric by two to three orders. We also report the tunability of TaN with Al doping, which is suitable for a p-type metal gate work function. Based on our results, several dual-gate integration processes by incorporating lanthanum or aluminum into a refractory metal nitride for CMOS technology are proposed.