Modeling and simulation of InAs/GaAs quantum dot lasers

Based on the analysis of carrier dynamics in quantum dots (QDs), the numerical model of InAs/GaAs QD laser is developed by means of complete rate equations. The model includes four energy levels and among them three energy levels join in lasing. A simulation is conducted by MATLAB according to the rate equation model we obtain. The simulation results of PI characteristic, gain characteristic and intensity modulation response are reasonable. Also, the relations between the left facet reflectivity of laser cavity and threshold current as well as modulation bandwidth are studied. It is indicated that the left facet reflectivity increasing can result in reduced threshold current and improved modulation bandwidth, which is in accordance with experimental results. The internal mechanism of QD lasers is fully described with the rate equation model, which is helpful for QD lasers research.     

高性能InAs/GaAs量子点外腔激光器

为了获得高性能的量子点外腔激光器(ECL),利用InAs/GaAs量子点Fabry-Perot(FP)腔激光器研制了光栅外腔可调谐ECL。对InAs/GaAs量子点ECL进行了一系列的性能测试,主要包括单模稳定性测试、单模调谐范围测试、阈值电流密度测试、无跳模连续调谐测试和输出功率测试。在室温条件下获得了24.6nm的连续调谐范围,覆盖波长从999.2nm到1 023.8nm,并且实现了波长无跳模连续调谐。在调谐范围内最低阈值电流密度为1 525A/cm2,而且在中心波长处获得的单模输出功率为15mW,单模边模抑制比(SMSR)高达35dB。研究结果表明,通过构建光栅外腔可以实现高性能的InAs/GaAs量子点ECL。     

1.43 /spl mu/m InAs bilayer quantum dot lasers on GaAs substrate

An edge emitting quantum dot (QD) laser at 1430 nm is demonstrated with a structure grown by molecular beam epitaxy on GaAs substrate. The active region is based on three InAs bilayer QDs embedded in a conventional AlGaAs/GaAs waveguide. The threshold current density is 134 A/cm/sup 2/. Output power of 23 mW per facet is achieved.     

Dynamics of InAs/GaAs quantum dot lasers epitaxially grown on Ge or Si substrate

Growing semiconductor laser sources on silicon is a crucial but challenging technology for developing photonic integrated circuits(PICs).InAs/GaAs quantum dot(Qdot)lasers have successfully circumvented the mismatch problem betweenⅢ–Ⅴmaterials and Ge or Si,and have demonstrated efficient laser emission.In this paper,we review dynamical characteristics of Qdot lasers epitaxially grown on Ge or Si,in comparison with those of Qdot lasers on native GaAs substrate.We discuss properties of linewidth broadening factor,laser noise and its sensitivity to optical feedback,intensity modulation,as well as mode locking operation.The investigation of these dynamical characteristics is beneficial for guiding the design of PICs in optical communications and optical computations.     

InAs/InP量子点激光器制备工艺研究

报道了通过化学湿刻蚀制备窄脊条InAs/InP量子点激光器的方法。激光器脊条主要是由半导体材料InGaAs和InP构成,通过选择合适配比的H2SO4∶H2O2∶H2O和H3PO4∶HCl腐蚀溶液和InP的腐蚀方向,在室温下选择性地腐蚀了InGaAs和InP,获得了窄脊条宽为6μm的量子点激光器。此激光器能够在室温连续波模式下工作,激射波长在光纤通信重要窗口1.55μm,单面最大输出功率超过12mW。     

Annealing behavior of InAs/GaAs quantum dot structures

We investigate the annealing behavior of InAs layers with different thicknesses in a GaAs matrix. The diffusion enhancement by strain, which is well established in strained quantum wells, occurs in InAs/GaAs quantum dots (QDs). A shift of the QD luminescence peak toward higher energies results from this enhanced diffusion. In the case of structures where a significant portion of the strain is relaxed by dislocations, the interdiffusion becomes negligible, and there is a propensity to generate additional dislocations. This results in a decrease of the QD luminescence intensity, and the QD peak energy is weakly affected.     

Reliability study of InAs/InGaAs quantum dot diode lasers

Ridge-waveguide lasers with an InAs/InGaAs quantum dot active region have been subjected to accelerated ageing at 65 and 85/spl deg/C. No sudden failure was found during the 2070 h test. Activation energy of 0.79 eV was estimated, suggesting the 40/spl deg/C-lifetime >10/sup 6/ h.     

Investigation into the InAs/GaAs quantum dot material epitaxially grown on silicon for O band lasers

InAs/GaAs quantum dot(QD)lasers were grown on silicon substrates using a thin Ge buffer and three-step growth method in the molecular beam epitaxy(MBE)system.In addition,strained superlattices were used to prevent threading disloca-tions from propagating to the active region of the laser.The as-grown material quality was characterized by the transmission electron microscope,scanning electron microscope,X-ray diffraction,atomic force microscope,and photoluminescence spectro-scopy.The results show that a high-quality GaAs buffer with few dislocations was obtained by the growth scheme we de-veloped.A broad-area edge-emitting laser was also fabricated.The O-band laser exhibited a threshold current density of 540 A/cm² at room temperature under continuous wave conditions.This work demonstrates the potential of large-scale and low-cost manufacturing of the O-band InAs/GaAs quantum dot lasers on silicon substrates.     

Optimisation of a-factor for quantum dot InAs/GaAs fabry-perot lasers emitting at 1.3 /spl mu/m

Dynamic measurements of the Henry factor alpha_H of InAs/GaAs Fabry-Perot lasers are compared for 3-, 5- and 10-QD layers. While alpha_H dramatically increases with the bias current for 3- and 5-QD stacks, it only amounts to <4 for the 10-layer stack at high currents, a value similar to that of QW-lasers     

Low threshold current operation of self-assembled InAs/GaAs quantum dot lasers by metal organic chemical vapour deposition

Low threshold current operation of self-assembled InAs/GaAs quantum dot lasers grown by metal organic chemical vapour deposition is reported. Continuous-wave lasing at room temperature with low threshold current (6.7 mA) was achieved at the wavelength of 1.18 /spl mu/m. The threshold current of 6.7 mA is the lowest value so far achieved in quantum dot lasers grown by metal organic chemical vapour deposition. Comparison with photoluminescence spectra indicates that the observed lasing originates from the ground state of InAs quantum dots.     

Capacitance spectroscopy of deep states in InAs/GaAs quantum dot heterostructures

The results of a study of a structure with a single array of InAs quantum dots in a GaAs matrix using capacitance-voltage measurements, deep-level transient spectroscopy (DLTS), photoluminescence spectroscopy, and transmission electron microscopy are reported. Clusters of interacting bistable defects are discovered in GaAs layers grown at low temperature. Controllable and reversible metastable populating of quantum-dot energy states and monoenergetic surface states, which depends on the temperature and conditions of a preliminary isochronal anneal, is observed. This effect is associated with the presence of bistable traps with self-trapped holes. The DLTS measurements reveal variation of the energy for the thermal ionization of holes from surface states of the InAs/GaAs heterointerface and the wetting layer as the reverse bias voltage is increased. It is theorized that these changes are caused by the built-in electric field of a dipole, which can be formed either by wetting-layer holes or by ionized levels located near the heterointerface. Fiz. Tekh. Poluprovodn. 33, 184–193 (February 1999)     

Coupling of electron states in the InAs/GaAs quantum dot molecule

Deep level transient spectroscopy (DLTS) is used to study electron emission from the states in the system of vertically correlated InAs quantum dots in the p-n InAs/GaAs heterostructures, in relation to the thickness of the GaAs spacer between the two layers of InAs quantum dots and to the reverse-bias voltage. It is established that, with the 100 Å GaAs spacer, the InAs/GaAs heterostructure manifests itself as a system of uncoupled quantum dots. The DLTS spectra of such structures exhibit two peaks that are defined by the ground state and the excited state of an individual quantum dot, with energy levels slightly shifted (by 1–2 eV), due to the Stark effect. For the InAs/GaAs heterostructure with two layers of InAs quantum dots separated by the 40 Å GaAs spacer, it is found that the quantum dots are in the molecule-type phase. Hybridization of the electron states of two closely located quantum dots results in the splitting of the levels into bonding and antibonding levels corresponding to the electron ground states and excited states of the 1s ⁺, 1s ^?, 2p ⁺, 2p ^?, and 3d ⁺ types. These states manifest themselves as five peaks in the DLTS spectra. For these quantum states, a large Stark shift of energy levels (10–40 meV) and crossing of the dependences of the energy on the electric field are observed. The structures with vertically correlated quantum dots are grown by molecular beam epitaxy, with self-assembling effects.     

InAs quantum dot photonic crystal lasers and their temperature dependence

We report on the demonstration of optically pumped photonic crystal lasers with InAs quantum dot active regions operating at room temperature near 1310 nm. Absorbed threshold pump powers as low as 25 /spl mu/W are observed. We also extract a characteristic temperature of 17 K, which is attributed to limitations caused by surface recombination.     

InAs/GaInAs quantum dot DFB lasers emitting at 1.3 μm

Singlemode operation of 1.3 μm InAs/GaInAs quantum dot lasers has been achieved using the concept of complex coupled distributed feedback. Mode selection was realised by laterally patterned metal gratings. At room temperature the lasers show stable singlemode emission with sidemode suppression ratios of up to 55 dB, threshold currents as low as 17 mA and output powers of up to 8 mW under continuous wave operation     

InAs/InGaAs/GaAs quantum dot lasers of 1.3 μm range with high(88%) differential efficiency

Multiple layers (up to 10) of InAs/InGaAs/GaAs quantum dots considerably enhance the optical gain of quantum dot lasers emitting around 1.3 μm. A differential efficiency as high as 88% has been achieved in these lasers. An emission wavelength of 1.28 μm, threshold current density of 147 A/cm², differential efficiency of 80%, and characteristic temperature of 150 K have been realised simultaneously in one device     

InAs/InP量子点激光器中欧姆接触合金层特性研究

合金层与InAs/InP量子点激光器的接触电阻对激光 器的性能有很大影响,而接触电阻的 大小与合金材料、退火温度和退火时间有关。本文采用Au/Ni/Au/Ge做InAs/InP量子点激光 器的欧姆接触合金层,通过改变退 火温度和退火时间调节量子点激光器中接触电阻的阻值。实验发现,退火时间对接触电阻的 改变不 大,但是提高退火温度却能极大地降低接触电阻的阻值。实验获得了Au/Ni/Au/Ge 合金层与InAs/InP量子点激光器最佳欧姆接触条件,通过矩阵传输法测得相应接触电阻率为 1.34×10－6 Ω·cm²。在此条件下,制备激射中心波长为 1.577μm的多模量子点 激光器,室温下单面最大输出功率达到和超过39mW。     

Photoelectric spectroscopy of InAs/GaAs quantum dot heterostructures in a semiconductor/electrolyte system

The photovoltaic effect in the semiconductor/electrolyte junction is an effective method for investigation of the energy spectrum of InAs/GaAs heterostructures with self-assembled quantum dots. An important advantage of this method is its high sensitivity. This makes it possible to obtain photoelectric spectra from quantum dots with high barriers for the electron and hole emission from quantum dots into the matrix even if the surface density of the dots is low (～10⁹ cm^?2). In a strong transverse electric field, broadening of the lines of optical transitions and emission of electrons and holes from quantum dots into the matrix directly from the excited states are observed. The effect of the photovoltage sign reversal was detected for a sufficiently high positive bias across the barrier within the semiconductor. This effect is related to the formation of a positive charge at the interface between the cap layer and electrolyte and of the negative charge on impurities and defects in the quantum dot layer.     

Low frequency noise spectroscopy in InAs/GaAs resonant tunneling quantum dot infrared photodetectors

We have studied the temperature dependence of low-frequency noise in InAs–GaAs resonant tunneling quantum dot infrared photodetectors (T-QDIPs). The noise in these devices has been investigated in the temperature range of 78–300 K. The noise spectrum showed a weak Lorentzian component superimposed upon the 1/f^γ spectrum. The change in the cut-off frequency of the Lorentzian was analyzed as a function of temperature. The activation energy of the trap associated with this Lorentzian was obtained as 0.155 eV, which is in good agreement with the energy of the lowest energy state in the quantum dot.     

Optical nonlinearities in a passive GaAs/GaAlAs multiple quantum well strain-induced waveguide

Nonlinear Fabry-Perot switching effects have been observed in a 400 μm long GaAs/GaAlAs MQW strain-induced waveguide resonator. Experimental evidence showing that the mechanism responsible for the switch has a negative coefficient in the refractive index nonlinearity is described; this rules out the possibility that heating could be the cause of the observed switching. However, thermal effects were always present in the background and became more prominent at slow input-power sweep rates. Bistability due to increased absorption has also been observed in a similar nonresonant waveguide structure, at slightly longer wavelengths.