Selective quantum-well intermixing in GaAs-AlGaAs structures using impurity-free vacancy diffusion

Abstract

Impurity-free vacancy disordering (IFVD) using SiO 2 and SrF 2 dielectric caps to induce selective quantum-well (QW) intermixing in the GaAs-AlGaAs system is studied. The intermixing rate of IFVD was found to be higher in n-i-p and intrinsic than in p-in structures, which suggests that the diffusion of the Group III vacancy is not supported in p-type material. Single-mode waveguides have been fabricated from both as-grown and bandgap-tuned double-quantum-well (DQW) laser samples. Propagation losses as low as 8.5 dB1cm 01 were measured from the bandgap-tuned waveguides at the lasing wavelength of the undisordered material, i.e., 860 nm. Simulation was also carried out to study the contribution of free-carrier absorption from the cladding layers, and the leakage loss induced by the heavily p-doped GaAs contact layer. It was found that the leakage loss contributed by the GaAs cap layer is significant and increases with wavelength. Based on IFVD, we also demonstrate the fabrication of multiple-wavelength lasers and multichannel wavelength division multiplexers using the one-step "selective intermixing in selected area" technique. This technique enables one to control the degree of intermixing across a wafer. Lasers with bandgaps tuned to five different positions have been fabricated on a single chip. These lasers showed only small changes in transparency current, internal quantum efficiency, or internal propagation loss, which indicates that the quality of the material remains high after being intermixed. Four-channel wavelength demultiplexers based on a waveguide photodetector design have also been fabricated. Photocurrent and spontaneous emission spectra from individual diodes showed that the absorption edge was shifted by different degrees due to the selective degree of QW intermixing. The results obtained also imply that the technique can be used in the fabrication of broad-wavelength emission superluminenscent diodes.

Properties of the SiO2- and SiNx-capped GaAs(100) surfaces of GaInAsN/GaAs quantum-well heterostructures studied by photoelectron spectroscopy and photoluminescence

“…2,5 It can be also understood why Ga atoms have stronger tendency to diffuse toward SiO 2 than SiN x films: it is energetically more favourable to form Ga-O than Ga-N. 19 Furthermore, the difference in the thermal expansion coefficients has been shown to affect also the Ga diffusion; namely, SiO 2 has about 10 times larger expansion coefficient than GaAs, whereas for SiN x /GaAs, the difference is clearly smaller. 11,14,17 As 3d spectra (Fig. 4) are similar for all samples, except for as-grown SiO 2 which includes a small As-oxide (þ3.5 eV) emission.…”

“…This agrees well with the previously proposed reason for the BS, namely, the formation of Ga vacancies in the GaAs surface area enhances the In diffusion between QW and surrounding material. 11,18,[20][21][22][23] Our observation can be clearly assigned to Ga diffusion into SiO 2 and SiN x , which leads to increased O-bonding and insulating environment for Ga atoms and simultaneously Ga-vacancy formation in the GaAs substrate. GaO Z formation is, therefore, associated with the Ga atoms that locate in SiO 2 and SiN x layers.…”

“…[1][2][3][4][5][6][7][8] In particular, silicon dioxide (SiO 2 ) and silicon nitride (SiN x ) layers are routinely deposited onto GaAs(100) and other III-V(100) semiconductors at different steps of device processing. [9][10][11] For example, these dielectrics are used for surface protection, electrical insulation in laser diodes, antireflection coatings, and distributed Bragg reflectors, and for selective quantum well (QW) intermixing. The previous studies of SiO 2 /and SiN x /GaAs junctions have revealed Ga diffusion into the insulators, [12][13][14] As diffusion into the insulators, 13 As-cluster formation due to nitridation and annealing of GaAs, 15 annealing-induced improvement of the interfaces, 15,16 and defect formation at high-temperature annealings.…”

Present Status of Impurity Free Vacancy Disordering Research and Application

“…了阱区 Ga 在薄膜中的溶解度 [19] 。 多 种 QWI 技 术 相 结 合 的 应 用 是 QWI 研 究 中 的 一 个 新 热 点 。 Peng 等 [22] 把 IFVD 和 IIID 结 合 起 来 进 行 QWI， 对外延片进行 P 离子注入之后再采用 PECVD 生长 SiO2 薄膜， 然后再进行快速退火， 虽然混杂效果略有 提升， 但是起主要作用的仍是离子注入。Chang 等 [23] [24] 。一般来说， 温度越高， 时间越长， 由于热膨胀系数的差别产 生压应力， 而且 Ga、 In、 As、 P 在高温下的不稳定性也促使其更快更多地进入介质膜中， QWI 越明显， 带隙蓝 移程度越大 [18] 。但是过大的蓝移量对器件的发光性能产生影响， 所以采用低于活化能的退火温度对混杂后 的外延片进行循环退火处理， 可以优化晶格质量， 使其发光强度上升 [25] 。 2) 其他介质膜 [11,[26][27][28]…”

Annealing of self-assembled InAs/GaAs quantum dots: A stabilizing effect of beryllium doping

“…9 Postgrowth thermal annealing has been widely used to improve the material quality. [10][11][12][13][14][15][16][17] Recent photoluminescence ͑PL͒ studies 18 imply that the p-doping of the GaAs barriers improves the thermal stability of QD heterostructures. However, it has remained unresolved what the optimum position of p-doping is.…”