Orientation dependent growth behaviour during hydride VPE regrowth of InP:Fe around reactive ion etched mesas

An investigation on the hydride vapour phase epitaxy (HVPE) growth of SI-InP : Fe on patterned surfaces indicates that iron incorporation does not always synchronize with the rate of growth. This is especially true in certain crystallographic directions,e.g., (1,− 1,0) where the growth rate is high. This phenomenon has been attributed to the local chemistry which limits the availability of iron or to a simple kinetically limited supply of iron when the growth rate is high. However, it is shown that by a two step procedure such a synchronization can be achieved. The proposed procedure which is applicable to reactive ion etched vertical mesas is tested on a laser mesa and the surrounding SIInP:Fe is found to provide good current confinement and high modulation performance.     

Temporally resolved selective regrowth of InP around [110] and [-110] mesas

Temporally resolved selective regrowth of InP around reactive ion etched [110] and [-110] directional mesas is studied by hydride vapor phase epitaxy at the growth temperatures of 600, 650, 685, and 700°C. The regrowth profiles are strikingly different depending upon the mesa orientation. The results are interpreted by invoking the difference in the bonding configurations of these mesas as well as the growth facility in a direction leading to the largest reduction of dangling bonds under the growth conditions. Various emerging planes during regrowth are identified and arehhl planes with initial values of 1/h ≤ 3 but ≥ 3 as the planarization is approached. Initial lateral growth defined as the growth away from the mesa at half of its height in the very first minute is a decreasing function of temperature when plotted as Arrhenius curves. Such a behavior is attributed to the exothermicity of the reaction and to an enhanced pyrolysis of PH₃ to P₂. The lateral growth rate is much larger than that on the planar substrate. This should be taken into account when regrowth of a doped layer (e.g. InP:Fe or InP:Zn) is carried out to fabricate a buried heterostructure device since the dopant concentration can be very much lower than the one optimized on the planar substrates.     

Uniformity in HgCdTe diode arrays fabricated by reactive ion etching

Two-dimensional, midwavelength infrared (MWIR) HgCdTe detector arrays have been fabricated using reactive ion etching (RIE). Detector-to-detector uniformity has been studied in the devices fabricated with CdTe- and ZnS-passivation layers. Mapping of the doping profile, passivant/HgCdTe interface electrical properties, and diode impedance-area product (R₀A_j) in a two-dimensional array of diodes has been carried out. Temperature and perimeter/area dependence of the dark current are studied to identify the bulk and surface current components. Maximum R₀A_j=2×10⁷ Θcm² was achieved in CdTe-passivated, 200×200 μm² diode arrays. It demonstrates that CdTe-passivated, RIE-processed HgCdTe is a feasible technology.     

Analysis of the propagation losses of InP/InGaAsP trench waveguides fabricated by focused ion beam

Focused ion beam was used to fabricate 2 mm-long, 4 μm-wide and 4 μm-deep multimode trench waveguides in InP/InGaAsP. An automated stitching method was developed to fabricate mm-long structures using alignment marks. The waveguides were sputtered or etched using I₂ at room temperature and 150 °C stage temperature. The propagation losses induced by the different fabrication techniques were measured and ranged between 50 and 82 dB/cm. A damaged layer with implanted Ga and the sidewall roughness are identified to be the most important causes for the losses. FIB is shown to be a single-step fabrication technique for rapid-prototyping of photonic structures in InP/InGaAsP.     

In-situ spectroscopic reflectometry for polycrystalline silicon thin film etch rate determination during reactive ion etchinc

Accurate film thickness monitors are important for the development of real-time feedback control of dry etch processes and are very useful for run-to-run process control and process diagnostics. Technologically important films such as polycrystalline Si, which can have process-dependent refractive indices and/or surface roughness, pose significant challenges for low-cost, high-speed film thickness measurement systems. We have used spectroscopic reflectometry (SR) to make accuratein-situ, high-speed film thickness measurements during plasma etching of polycrystalline Si. The SR system determines the film thickness using a least squares regression algorithm that fits the theoretical reflectance to the experimental reflectance vs wavelength data. We have included physically based models for the variation of the polycrystalline Si bulk refractive indices and surface roughness in the fitting procedure. The parameters of the refractive index models are adjusted at the beginning of each run to account for wafer-to-wafer variationswithout the use of additional ex-situ measurements. We have usedex-situ spectroscopic ellipsometry to validate the models used and to check the accuracy of our SR measurements. Currently, our SR system can acquire data in 40 ms and the software can calculate the polycrystalline Si thickness in less than 55 ms per measurement, so that a new film thickness and etch rate estimate can be obtained in less than 100 ms. The methods used for analysis of polycrystalline Si are also directly useful for improving the accuracy of microscope-based spectral reflection measurement systems commonly used for in-line measurements. Using similar optical modeling concepts, the SR technique can also be used to accurately measure film thicknesses and etch rates of other thin films with process-dependent optical constants, such as deposited dielectrics and compound semiconductors.