Dynamic power density, wavelength, and switching time modulation of optically triggered power transistor (OTPT) performance parameters

Optical modulation by varying the intensity, wavelength, or switching time can dynamically alter the performance parameters of direct optically controlled power semiconductor device. Understanding the effect of optical parameters on these parameters from a first principle approach is necessary for making optimal design choices and gaining design insights. We focus on performance parameters whose variations with direct optical modulation have not been reported previously for a power semiconductor such as switching times and on-state resistance. We carry out analytical modeling and two-dimensional (2D) finite-element simulations for a GaAs/AlGaAs based superjunction lateral optically controlled power transistor that has been fabricated and successfully tested for high-voltage capability. It is shown that optical power density can modulate on-state resistance and more importantly the trade-off curve between breakdown voltage and on-state resistance. A closed-form analytical equation relating switching times with optical parameters via logarithmic function is derived and the nonlinear variation of on-state resistance and switching time with optical wavelength is illustrated. We also derive the analytical expression for power device rise time as a function of optical signal rise time and show that they are related by Lambert's W-function with exponential coefficients.     

Time-resolved photoluminescence of delta-doped AlGaAs/GaAs heterostructures

The photoluminescence (PL) at low temperature of three delta-doped AlGaAs/GaAs heterostructures is investigated under continuous and pulsed excitations. The PL under continuous excitations allows the identification of the trapping centres and probes the carrier's transfer to the GaAs channel. The time-resolved photoluminescence (TRPL) inquires about carrier dynamics and gives radiative lifetimes of different levels. The DX level shows two time constants of the intensity decay relating the splitting of the valence band under impurity strains which reduce the crystal symmetry. The two time constants evolve with temperature and exhibit an increase near T=50 K.     

MOCVD of AlGaAs/GaAs with novel group III compounds

The MOCVD of AlGaAs and GaAs from coordinatively saturated group III source materialsi.e. 1–3-dimethyl-aminopropyl-l-galla-cyclohexane ((C₅H₁₀)Ga(C₂N(CH_{3 2}) and the corresponding Al compound) was investigated. It was demonstrated that these precursors, which are inherently free of alkoxy contamination, are suitable for epitaxial growth of GaAs layers and structures of GaAs/AlGaAs. For comparison, data achieved with TEA (Al(C₂H₅)₃) or TⁱBA (Alⁱ(C₄H₉)₃) and TEG (Ga(C₂H₅)₃) are presented. A basic finding of this study is that due to the low thermal stability of TEA, TⁱBA and TEG the layers grown from these compounds suffer from insufficient homogeneity of layer thickness and composition. In contrast, the coordinatively saturated compounds show a reactivity suitable for large area growth. Additionally, intrinsic impurity (N, C) uptake appears to be low and electrical as well as PL data show the satisfactory quality of GaAs and AlGaAs layers grown from this new type of precursors. Specifically, a reduction of oxygen incorporation compared to growth from the standard trialkyls is indicated by PL measurements on layers grown at different temperatures.     

Carbon tetrachloride doped Al x Ga1−x As grown by metalorganic chemical vapor deposition

A dilute mixture of CCl₄ in H₂ has recently been shown to be a suitable carbon doping source for obtainingp-type GaAs grown by metalorganic chemical vapor deposition (MOCVD) with carbon acceptor concentrations in excess of 1 × 10¹⁹cm⁻³. To understand the effect of growth parameters on carbon incorporation in CCl₄ doped Al _x Ga_1−x As, carbon acceptor concentration was studied as a function of Al composition, growth temperature, growth rate, and CCl₄ flow rate using electrochemical capacitance-voltage profiling. The carbon incorporation as a function of Al composition, growth temperature and CCl₄ flow rate was also measured by secondary ion mass spectroscopy (SIMS). All layers were grown by low pressure MOCVD using TMGa and TMAl as column III precursors, and 100% AsH₃ as the column V source. Increased Al composition reduced the dependence of carbon concentration on the growth temperature. Reduced growth rate, which resulted in substantially decreased carbon acceptor concentrations in GaAs, had an insignificant effect on the carrier concentration of Al_0.4Ga_0.6As. A linear relationship between hole concentration and CC1₄ flow rate in Al_xGa_1−x As for 0.0 ≤x ≤ 0.8 was observed. These results are interpreted to indicate that adsorption and desorption of CCl _y (y ≤ 3) on the Al _x Ga_1-x As surface during crystal growth plays an important role in the carbon incorporation mechanism.     

Design and process development of a novel multi-wafer OMVPE reactor for growing very uniform GaAs and AlGaAs epitaxial layers

A unique multi-wafer OMVPE reactor with capability to produce atomic-layer abrupt-ness is demonstrated. Uniform GaAs and AlGaAs epitaxial layers were grown on four two-inch wafers or one three- or four-inch wafer. Thickness variation across a three-inch wafer was less than ±2%, while the variation of Al solid composition was less than ±1%. Multiple AlGaAs/GaAs quantum wells ranging in size from 10Å to 140Å were grown with heterointerface roughness less than one monolayer. The electrical properties of HEMT device were studied. Variations of sheet carrier concentration and electron mobility were ±6% and ±5% respectively across a three-inch wafer. The carrier con-centration profile, mobility spectrum and device characteristics of DH-HEMT are also presented. These results indicate that this OMVPE reactor can grow good device struc-tures for microwave and millimeter-wave power device applications.     

新结构雪崩光探测器的特性仿真及后工艺优化

报道了一种在倍增区引入AlxGa1-xAs带隙梯度结构的谐振腔增强型雪崩光探测器,并提出优化其后工艺制作的新方法.通过将Al0.4Ga0.6As(28 nm)一Al0.2Ga0.8As(10 nm)-GaAs(50 nm)带隙梯度结引入雪崩探测器的高场区,可以实现对探测器噪声和频率响应两个主要性能的优化.数值仿真表明,该结构探测器具有较小的噪声(有效离化系数为0.1),约33 GHz的3 dB带宽(增益为5),在增益为15时可获得420 GHz的增益带宽积.在实际的后工艺制作中,提出使用苯并环丁烯树脂进行InP/空气隙DBR反射镜与雪崩探测器结构粘合的方法,简化了工艺流程.

摘要：

     

Free standing modulation doped core–shell GaAs/AlGaAs hetero‐nanowires

Modulation doped AlGaAs/GaAs core–shell nanowire structures were grown by molecular beam epitaxy. A Si delta‐doping was introduced in the AlGaAs shell around the {110} facets of the GaAs core. The wires are typically highly resistive at low temperatures. However, they show a pronounced persistent photoconductivity effect indicating activation of free carriers from the delta‐doped shell to the GaAs core. The n‐type character of the channel is demonstrated by applying a back‐gate voltage. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron paramagnetic resonance and optically-detected magnetic resonance of donors in AlxGa1-xAs

The Electron Paramagnetic Resonance (EPR) and Optically-Detected Magnetic Resonance (ODMR) work on Si-donors in Al _{x Ga1- x} As is reviewed in the context of the shallow-deep bistability (DX) problem. Three donor states are important. Little work has been published on donors tied to theT-minimum. However, there are many results forX-donors. In AlAs/GaAs heterostructures, well-resolved spectra reveal a donor state comprised of independentX _x andX _y valleys with theXz valley unpopulated due to the hetero-epitaxial strain. As Al mole fraction decreases, intervalley coupling is evident from the line positions and linewidths. The published attempts to observe and identify the deep (relaxed) state are inconclusive. Some suggestions for future work are presented.     

Confirmation of large lattice relaxation of theDX center by extended photo-ionization cross-section measurements

Although the large lattice relaxation model (LLR) for electron capture at the donor relatedDX center in Al_xGa_1-xAs has seen wide acceptance over the last 12 years, there have been some recent proposals which have attempted to explain the experimental data with models that only require small lattice relaxation (SLR). One key piece of evidence supporting LLR is the large observed difference (in the case of Si-doped Al_xGa_1-xAs) between the optical (∼1.4 eV) and thermal (∼0.2 eV) ionization energies. The SLR model proposed that the lowest energy optical ionization was a very weak process, and that the optical transition which had been observed previously is a transition to a higher band. These arguments were supported by photoconductivity data showing a finite photo-ionization rate at energies as low as 200 meV. To resolve this question we have measured the photo-ionization cross section over 7 to 8 orders of magnitude using a tunable infrared laser as a source. A consistent optical ionization energy of about 1.4 eV was observed for 4 samples of differing alloy compositions and doping levels.In no case was there any detectable photo- ionization below 0.8 eV. A detailed discussion of these experiments examines the difficulty in obtaining such a large dynamic range optical spectrum. Of particular relevance are the issues of ionization detection, and the brightness of purity of the optical source. A thorough review of these issues and their impact on previous studies of theDX center is presented.     

在MOCVD外延生长中Ⅴ/Ⅲ比对AlxGa1-xAs外延层中A1组分分布的影响

本实验首次观察到用MOCVD方法在GaAs基片上外延生长AlxGa1-xAs/GaAs薄膜结构时,生长中所用的Ⅴ/Ⅲ比对外延层中Al组份x的分布的影响.当Ⅴ/Ⅲ比较低时,外延层中的Al组份出现很明显的层状阶梯形三层分布:靠近基片的一层中x值较低,而在外延层的表面层中x值较高.随着生长中所用的Ⅴ/Ⅲ比增加时,Al组份的分布趋于均匀.利用GaAs的高温热分解和Ga、As离子在晶体中的热扩散及其对外延生长的影响,对这一现象作了初步解释.