Temperature Distribution in Ridge Structure InGaN Laser Diodes and Its Influence on Device Characteristics

Time-dependent thermal simulation of ridge-geometry InGaN laser diodes is carried out with a two-dimensional model. A high temperature in the waveguide layer and a large temperature step between the regions under and outside the ridge are generated due to the poor thermal conductivity of the sapphire substrate and the large threshold current and voltage. The temperature step is thought to have a strong influence on the characteristics of the laser diodes. Time-resolved measurements of light-current curves,spectra, and the far-field pattern of the InGaN laser diodes under pulsed operation are performed. The results show that the thermal lensing effect improves the confinement of the higher order modes and leads to a lower threshold current and a higher slope efficiency of the device while the high temperature in the active layer results in a drastic decrease in the slope efficiency.

高线性度外延及注入GaAs Hall器件

讨论了外延及注入制作的薄层GaAs Hall器件如何获得高的磁线性度。GaAs Hall器件的磁线性度在高磁场下会有偏离，但可以通过外延及注入的过渡层对有源区进行补偿，在合适的有源区和过渡区的浓度和厚度分布中，可以得到在2.5T的强磁场下，±0.04%的高磁线性度。

Wavelength tunable electroabsorption modulated DFB baser with thin film heater

　

Optical transitions and type-II band lineup of MBE-grown GaNAs/GaAs single-quantum-well structures

We have investigated transitions above and below band edge of GaNAs/GaAs and InGaNAs/GaAs single quantum wells (QWs) by photoluminescence (PL) as well as by absorption spectra via photovoltaic effects. The interband PL peak is observed to be dominant under high excitation intensity and at low temperature. The broad luminescence band below band edge due to the nitrogen-related potential fluctuations can be effectively suppressed by increasing indium incorporation into InGaNAs. In contrast to InGaNAs/GaAs QWs, the measured interband transition energy of GaNAs/GaAs QWs can be well fitted to the theoretical calculations if a type-II band lineup is assumed. (C) 2001 Elsevier Science B.V. All rights reserved.

Structural and infrared absorption properties of self-organized InGaAs GaAs quantum dots multilayers

Self-organized InGaAs/GaAs quantum dots (QDs) stacked multilayers have been prepared by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy shows that the InGaAs QDs are nearly perfectly vertically aligned in the growth direction [100]. The filtering effect on the QDs distribution is found to be the dominant mechanism leading to vertical alignment and a highly uniform size distribution. Moreover, we observe a distinct infrared absorption from the sample in the range of 8.6-10.7 mu m. This indicates the potential of QDs multilayer structure for use as infrared photodetector.

长白山北坡灌木阔叶红松林定位动态分析

灌木阔叶红松林做为长白山地区的主要地域性顶极群落，其相对稳定程度一直受到有关人士的关注。笔者通过其固定标准地长期观测资料的分析，探讨其中龄林阶段、近熟林阶段、以及从中龄林演替到近熟林过程中，该类型森林生态系统的动态规律。首先，在中龄林（建群种红松的优势木年龄约为170年）阶段的十年动态规律是：在林冠层中，立木总株数显著增多，其中槭树和椴树株数激增现象尤为明显。枯倒木树种有限（仅四种），且大、中、小径级枯倒木株数比为3:5:15，中、小径级枯倒木多为砸倒木。种群平均胸径除槭树、椴树和榆树出现负增长外，余者均有所增大。立木树冠相对高度变化不明显，红松立木大多仍处于被压冠状态。总生物量由305.40吨/公顷增343.04公顷，其中各种群生物量均有不同程度的增加。十年中，因枯倒木而使其总生物量损失了9.18吨/公顷。群落更新状况不良。十年中更新幼苗幼树的保存率极低，且总株数由4775株/公顷降至3700株/公顷。其中红松更新尤为恶化。群落中灌木和草本植被的生物量，无论是地上部分还是地下部分，均略有增大趋势。在其土壤层中，浅层的发生有机养分富积现象显著。其降水和气温变化状况为：降水和温度的林、内外年变化规律正相关性较强，且林内均低于林外。降水和气温的年代变化规律不明显。其次，在近熟林（建群种红松的优势木年龄约为260年阶段其林冠层九年动态规律为：活立木总株数增加稀少，红松、蒙古栎和榆树的株数均保持相对而言稳定。枯树木树种较多（仅蒙古栎未发生枯倒），且大、中、小径级枯倒木株数之比为8：4：8，其中风倒和病腐枯倒木所占比重较大。各种群平均胸径和平均冠幅均有所增大。红松树冠具有冲破上层阔叶树冠进入林冠层上层的趋势。总蓄积具增大趋势，种群蓄积除白桦外均有所增大。总生物量由342.64吨/公顷增至355.45吨/公顷，其中槭树、椴树和白桦的生物量受枯倒木的影响，出现负增长现象。最后，群落由中龄林演替至近熟林过程中的动态规律是：在林冠层，活立木总株数减少趋势显著，但种群按株数多少排序的结构变化不大。枯倒木的树种有增多趋势，且其平均胸径由25.13厘米升至31.69厘米。种群平均胸径和平均冠幅均有增大趋势。总蓄积量505.34立米米/公顷升至524.00立方米/公顷。总生物量由343.04吨/公顷增至355.45吨/公顷，其平均年增长量有明显的趋势。在演替层，立木种类和株数均有减少趋势，使得结构较简单的演替层更趋于简单化。在该层中，未发现建群种红松的存在。总生物量由2.64吨/公顷降至2.44吨/公顷。在更新层，更新状况由不良趋于恶化。幼苗树总株数由3846株/公顷降至2946株/公顷，其中红松更新株数所占比重趋于减少至零。在灌木层，灌木总株数由6125株/公顷降至5575株/公顷，其中大灌木株数增多，而小灌木株数减少。毛榛子于灌木层中株数所占比重最大，由33%升至42%。总生物量由2.85吨/公顷升至4.85吨/公顷。在草本层中，草本植被的种类，总株数和总盖度均有增多或增大的趋势。总生物量由0.77吨/公顷升至1.04吨/公顷。群落的总生物量由349.28吨/公顷升至363.78吨/公顷。在土壤层中，有机养分在浅层的发生层中富积现象较显著，且其浅层发生层的酸度有减弱至趋于中性的趋势。本文的动态分析不仅为该林型动态数学模型的建立和检验提供了更为可靠的依据，同时对于其经营措施的制定具有一定的科学价值。