Broadband PureGaB Ge-on-Si photodiodes responsive in the ultraviolet to near-infrared range

Optical characterization of PureGaB germanium-on-silicon (Ge-on-Si) photodiodes was performed for wavelengths between 255 nm and 1550 nm. In PureGaB technology, chemical vapor deposition is used to grow germanium islands in oxide windows to the silicon substrate and then cap them in-situ with nm-thin layers of first gallium and then boron, thus forming nm-shallow p+n diodes. These PureGaB Ge-on-Si photodiodes are CMOS compatible and characterized by low leakage currents. Here they are shown to have high responsivity in the whole ultraviolet (UV) to near infrared (NIR) wavelength range. Particularly, two sets of diodes were studied with respect to possible detrimental effects of the Al metallization/alloying process steps on the responsivity. Al-mediated transport of the Ge and underlying Si was observed if the PureGaB layer, which forms a barrier to metal layers, did not cover all surfaces of the Ge islands. A simulation study was performed confirming that the presence of acceptor traps at the Ge/Si interface could decrease the otherwise high theoretically attainable responsivity of PureGaB Ge-on-Si photodiodes in the whole UV to NIR range. A modification of the device structure is proposed where the PureGaB layer covers not only the top surface of the Ge-islands, but also the sidewalls. It was found that to mitigate premature breakdown, it would be necessary to add p-doped guard rings in Si around the perimeter of Ge islands, but this PureGaB-all-around structure would not compromise the optical performance.</p

Лавинные светодиоды на основе наноструктурированного кремния для оптических межсоединений

The paper analyzes the parameters of silicon avalanche LEDs and their use for electron-optical signal transmission systems. The advantages of silicon avalanche LEDs are shown, among which high speed and compatibility with silicon technology should be highlighted. Experimental avalanche LEDs based on nanostructured silicon were fabricated and studied. The results of controlling the electroluminescence spectrum of avalanche LEDs due to the choice of production conditions to form nanostructured silicon are presented. It was found that the temperature of the substrate during the deposition of the surface nanocomposite aluminum + silicon film affected the size of the formed silicon nanoparticles determining the spectral characteristics of avalanche LEDs. This allows shifting the maximum of their emission spectrum to a shorter wavelength region of the visible range due to the forming of smaller silicon nanoparticles. The authors have developed an optical interconnection system consisting of avalanche LEDs based on nanostructured silicon and a microchannel silicon wafer used to transmit a light signal. The study of various operating modes of the developed optoelectronic system was performed and an increase in the efficiency of optocouple based on avalanche LEDs to 0.2% due to the pulsed operating mode was achieved. It is shown that the efficiency of the optocouple increases with LED current and it is the pulsed mode of its operation that is characterized by the maximum current, which is due to more efficient removal of Joule heat in the intervals between pulses, ensuring stable operation of the entire system. The results obtained open up new opportunities for the development of optical interconnections between silicon chips and silicon optoelectronics in general.В работе проведен анализ параметров кремниевых лавинных светодиодов и их использования для электронно-оптических систем передачи сигналов. Показаны преимущества данных приборов, среди которых следует выделить высокое быстродействие и совместимость с кремниевой технологией. Изготовлены экспериментальные образцы лавинных светодиодов на основе наноструктурированного кремния и исследованы их структурные и оптические характеристики. Представлены результаты управления спектром электролюминесценции лавинных светодиодов за счет выбора технологических режимов формирования наноструктурированного кремния. Установлено, что температура подложки в процессе осаждения поверхностной нанокомпозитной пленки алюминий + кремний влияет на размеры формирующихся кремниевых наночастиц, определяющих спектральные характеристики лавинных светодиодов. Это позволяет смещать максимум спектра их излучения в более коротковолновую область видимого диапазона за счет формирования кремниевых наночастиц меньших размеров. Разработана система оптических межсоединений, состоящая из лавинных светодиодов на основе наноструктурированного кремния и микроканальной кремниевой пластины, используемой для передачи светового сигнала. Проведено исследование различных режимов функционирования разработанной оптоэлектронной системы и достигнуто увеличение эффективности оптопары на основе лавинных светодиодов до 0,2 % за счет импульсного режима функционирования. Показано, что эффективность оптопары увеличивается при увеличении тока светодиода, и именно импульсный режим его работы характеризуется максимальным значением тока, что обусловлено более эффективным отводом джоулевого тепла в промежутках между импульсами, обеспечивающим стабильную работу всей системы. Полученные результаты открывают новые возможности для развития оптических межсоединений между кремниевыми чипами и кремниевой оптоэлектроники в целом

Reverse breakdown and light-emission patterns studied in Si PureB SPADs

The relationship between light-emission patterns from silicon avalanche-mode light-emitting diodes (AMLEDs), and avalanche breakdown was investigated using photodiodes fabricated in pure boron (PureB) technology. The quality of the diodes ranged from high-quality, low dark-current devices with abrupt breakdown characteristics that were suitable for operation as single-photon avalanche diodes (SPADs), to diodes with gradually increasing reverse currents before actual breakdown. The reverse I-V characteristics were measured and correlated to light-emission data obtained simultaneously using a PureB photodetector, and inspected using a camera with which distinct emission patterns could be identified. When increasing the voltage far past breakdown, light emission invariably becomes dominant at the photodiode periphery. Based on the examination of a large variety of anode geometries, it is concluded that the most efficient light emission per consumed power is achieved with defect-free narrow-anode diodes that also are applicable as low-dark-count-rate SPADs