Efficient TE-Selective P-I-i-I-N GaAs/Al 0.35Ga0.65As Waveguide Phase Modulator at λ=1.55μm

We fabricated a phase modulator with significant phase shift for TE mode but negligible for TM mode. The measured phase shift efficiency was 7.9 /V mm for TE mode. No modulation was observed for TM mode.     

Negative and persistent photoconductivity in p-type Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As heterostructures under uniaxial stress

Abstract

Illumination of a double p-Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As heterostructure by a red light emitting diode results in a negative photoconductivity that, after the diode is switched off, slowly relaxes to a positive persistent photoconductivity, characterised by an approximately 1.5-fold increase of the two-dimensional hole concentration. This metastable state may be explained with a model in which deep electron traps are supposed to be located above the Fermi level on the inverted heterointerface. Under uni-axial compression the hole concentration in the persistent photoconductivity state, as well as in the dark state, demonstrates the same linear decrease.     

Sulfur diffusion into GaAs/Ga0.7Al0.3As heterostructures for device applications

0.7 Al_0.3As heterostructure layers grown by liquid phase epitaxy. GaS and As in a weight ratio of 2:1 were used as the diffusion sources. The source of GaS was carefully selected via X-ray diffraction analysis. Sulfur diffusion was carried out in a sealed quartz ampoule at a temperature of 820 °C and an arsenic pressure of 1 atmosphere. The carrier concentration profile from experimental results agrees well with the theoretical profile, which was calculated with the complementary error function solution assuming a segregation coefficient of m=1 at the hetero-junction interface. A smooth diffusion of sulfur was observed without any surface damage or hetero-interface defects. A double heterostructure laser was fabricated by employing sulfur diffusion. Cathode luminescence intensity analysis revealed that no damage was caused by sulfur diffusion at the active layer. Excellent characteristics such as a long life, a low threshold current, a fundamental transverse mode oscillation and a high modulation speed were obtained. Received: 1 June 1998/Accepted: 10 August 1998     

Spin orientation by optical pumping of strained In0.35Ga0.65As/GaAs quantum wells grown on vicinal substrates

Strained In_0.35Ga_0.65As/GaAs quantum wells of various thicknesses grown on vicinal substrates were studied by optical pumping techniques. From the 4K photoluminescence and photoluminescence excitation results we found that a blue shift of the excitonic lines and an improvement of the optical properties of the samples accompany the misorientation of the substrate. The influence of Indium surface segregation was taken into account to fit the experimental results. The dependence of the circular degree of polarization on the excitation energy allows us to determine the nature of the (11h-1e) transition and to evidence a localization of the excitons on the terraces existing at the interfaces. It was not possible to evaluate the characteristic times governing the photoluminescence polarization.     

Energy sublevels in an Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As quantum wire

We report the successful fabrication of a V-grooveAl_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As quantum wire system and the temperature-dependent photoluminescence (PL) measurement. The PL spectra are dominated by four features at 681, 642, 635 and 621 nm attributed to the luminescences from quantum wire, top, vertical and side-wall well regions by micro-PL measurements. By the calculations of the energy structure, discrete states (localized sublevels) in the quantum wire region and continuum states (extended along the side-wall and vertical quantum wells) in side-wall and vertical quantum wells have been obtained in both the conduction and valence bands. The calculated excitation energies explain very well the peak positions and their temperature dependence in the photoluminescence measurements.     

Weak localization in Al0.25Ga0.75As/In0.2Ga0.8As/GaAs wires

The phase coherence length L_Ø, its temperature dependence and the spin-orbit scattering length L_SO in Al_0.25Ga_0.75As/In_0.2Ga_0.8As/GaAs wires fabricated by electron-beam lithography and CH₄/H₂ Reactive Ion Etching (RIE), were extracted by fitting a 1-dimensional weak localization theory to two-terminal measurements in the temperature range between 2 K and 50 K. The scattering mechanism was found to be Nyquist (electron-electron collisions with small energy transfer).     

p型GaN/Al0.35Ga0.65N/GaN应变量子阱中二维空穴气的研究

对Ga面p型GaN/Al0.35Ga0.65N/GaN应变异质结构中形成的二维空穴气(2DHG)进行了研究.首先基于半导体-绝缘体-半导体异质结构模型确定了应变异质中的临界厚度,然后自洽求解薛定谔方程和泊松方程,计算了当中间势垒层AlGaN处于完全应变状态和半应变状态两种条件下,顶层GaN及中间层AlGaN厚度的变化对2DHG分布的影响.计算结果表明,势垒层AlGaN和顶层GaN的应变状态和厚度对极化引起的2DHG面密度及分布有重要影响.在此基础上制备了p型GaN/Al0.35 Ga0.65N/GaN应变量子阱结构肖特基器件,并通过器件的C-V测试证实了异质结处2DHG的存在.器件响应光谱的测试结果表明,由于p型GaN/Al0.35Ga0.65N/GaN量子阱中强烈的极化作用和Stark效应使得器件零偏压和反向偏压时的响应光谱都向短波方向移动了10 nm,在零偏压下器件在280 nm处的峰值响应为0.022 A/W,在反向偏压为1 V时,峰值响应达到0.19 A/W,已经接近理论值.     

双δ掺杂In0.65Ga0.35As/In0.52Al0.48As赝型高迁移率晶体管材料子带电子特性研究

研究了基于InP基的In0.65Ga0.35As/In0.52Al0.48As赝型高迁移率晶体管材料中纵向磁电阻的Shubnikov-deHaas(SdH)振荡效应和霍耳效应,通过对纵向磁电阻SdH振荡的快速傅里叶变换分析,获得了各子带电子的浓度,并因此求得了各子带能级相对于费米能级的位置.联立求解Schrdinger方程和Poisson方程,自洽计算了样品的导带形状、载流子浓度分布以及各子带能级和费米能级位置.理论计算和实验结果很好符合.实验和理论计算均表明,势垒层的掺杂电子几乎全部转移到了量子阱中,转移率在95%以上.     

Spectroscopic investigation of many-body effects in GaAs/Al x Ga1−x As superlattices

Summary We report a systematic study of the many-body interactions induced by quasi-stationary intense optical pumping in semiconductor superlattices of GaAs/Al _x Ga_1−x As. Spontaneous and stimulated luminescence and optical-gain measurements performed at different temperatures and with several exciting wavelengths allow us to observe band filling effects and optical amplification in these 2D structures. Hotcarrier quasi-equilibrium distribution and band gap renormalization effect the spontaneous-emission line shapes; excitonic interactions slightly blueshift the emission lines. The spectra have been interpreted as a consequence of the electron hole plasma occurring which mainly recombines at the quantized exciton energies. Optical-gain measurements have shown a gain factor which remains constant up to about 140K and is higher than the one measured in three-dimensional GaAs crystals. In a superlattice having aluminium concentration near the direct-indirect crossover, quasiresonant optical pumping in the well has shown a new spectral feature in the stimulated emission which has been tentatively ascribed to a Γ-X mixing of the electronic wave functions in the well and in the barrier.

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Riassunto Viene presentato uno studio sistematico delle interazioni a molti corpi indotte da pompaggio ottico, inteso in condizioni quasi stazionarie, in supereticoli di GaAs/Al _x Ga_1−x As. Misure di luminescenza spontanea e stimolata e di guadagno ottico in un ampio intervallo di temperature e con diverse lughezza d'onda di eccitazione hanno messo in evidenza effetti di ?band-filling? e di amplificazione ottica. Gli effetti dei processi di rilassamento da elettroni caldi, della rinormalizzazione della gap e delle interazioni eccitoniche sono discussi sulla base delle forme di riga della luminescenza. Gli spettri sono interpretati come la conseguenza della fotogenerazione di un plasma elettrone-buca che ricombina alle energie degli eccitoni quantizzati. Le misure di guadagno ottico mostrano un fattore di guadagno maggiore che nel semiconduttore tridimensionale e che resta costante sino a circa 140 K. In un supereticolo con concentrazione di alluminio prossima al ?cross over? diretto-indiretto, il pompaggio ottico risonante con gli stati nella buca di potenziale ha mostrato una nuova banda di emissione attribuita agli effetti delΓ-X mixing delle funzioni d'onda elettroniche nella buca e nella barriera.

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Резюме Мы систематически исследуем многочастичные взаимодействия, индуцированные квазистационарной интенсивной оптической накачкой в полупроводниковых суперрешетках GaAs/Al_xGa_1−xAs. Измерения спонтанной и стимулированной люминесценции и оптического усиления, проведенные при различных температурах и при нескольких длинах волн возбуждения, позволяют нам наблюдать эффекты заполнения зон и оптического усиления в этих 2D структурах. Квазиравновесные распределение горячих носителей и перенормировка ширины запрещенной зоны влияют на формы линий спонтанного излучния. Экситонные взаимодействия вызывают голубое смещение линий излучения. Полученные спектры интерпретируются, как следствие электрон-дырочной плазмы, которая, в основном рекомбинирует прп кванрованных экситонных энергиях. Измерения оптического усиления определяют коэффициент усиления, который остается постоянным вплоть до 140 K, и оказывается бодьше, чем измеренный в трехмерных кристлллах GaAs. В суперрешетке, имеющей концентрацию алюминия вблизи прямого-косвенного кроссовера, квазирезонансная оптическая накачка обнаруживает новую спектральную особенность в стимулированном излучении, котоая приписывается смешиванию электронных волновых функций в яме и в барьере.

     

Dependence of propagation loss on etching depth in Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As strip-loaded type waveguides

Al_0.3Ga_0.7As/GaAs/Al_0.3Ga_0.7As strip-loaded waveguides were fabricated using a broad-beam electron cyclotron resonance (ECR) ion source. It was found that a very smooth etching profile can be obtained by ECR ion etching and the etching rate of Al_0.3Ga_0.7As is 70 nm min^-1. The propagation losses of strip-loaded type III–V compound semiconductor waveguides with various etching depths were studied by the Fabry-Perot cavity method. It was observed that the reflectance at the cleavage increases slightly with etching depth for TE polarization. The propagation loss is measured as 1.5 dB cm^-1 for etching depth of 0.7 m, less than 1 dB cm^-1 for 0.8 m, and 3.5 dB cm^-1 for 1.1 m.     

Scaled nano-and microrelief of ordering regions in Al x Ga1 − x As/GaAs(100) epitaxial heterostructures

The Al _x Ga_{1 ? x} As/GaAs(100) heterostructures grown by MOS hydride epitaxy were studied using atomic force and scanning electron microscopy. Regions with an ordered nanorelief with a period of approximately 115 nm were discovered on the surface of the sample with x ～ 0.50. An AlGaAs₂ superstructural phase appears in these regions.     

Optical investigations of GaAs/Ga1−x Al x As Quantum wells grown by molecular-beam epitaxy

Summary Measurements of photoluminescence, excitation photoluminescence and reflectance are performed at various temperatures on a series of GaAs/Ga_1−x Al _x As quantum well structures grown by molecularbeam epitaxy. The selective photoluminescence data of the GaAs buffer layers are analysed in order to correlate the optical properties with the growth conditions. The Stokes shift of the excitation emission line from quantum wells is investigated under various excitation conditions. A considerable decrease of the Stokes shift is observed in the case of nonresonant and intense excitations. Also the extrinsic photoluminescence, as well as its temperature dependence, are interpreted. In addition, the temperature effects on both the bulk and quantum well spectra are shown to clarify the excitation features and the contribution of the interband transitions. To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.     

Acoustic phonon dephasing in shallow GaAs/Ga Al As single quantum wells

The intermediate dimensionality regime is studied on a set of shallow GaAs/Ga Al As single quantum wells. Such heterostructures exhibit 2D strong excitonic electroabsorption together with near 3D fast transport properties. We report dephasing time measurements of the heavy-hole exciton and we show that the acoustic phonon contribution decreases with to a value in good agreement with theoretical predictions for GaAs bulk.