Be-ion implanted p-n InSb diode for infrared applications. Modeling, fabrication and characterization

Transport theory for modeling the electric characteristics of high-quality p-n diodes has been developed. This theory takes into account a non-uniform profile of p- doping, finite thickness of the quasi-neutral regions and possible non-uniformity of the bulk recombination coefficient. The theory is based on related solutions of the Poisson equation, drift-diffusion equation and continuity equation with a generation-recombination term taking into account the simple band-to-band generation/recombination model. We have ascertained that the non-uniform profile of p-doping can lead to formation of p-n junctions with a specific two-slope form of the electrostatic barrier and two regions with the high built-in electric fields. We have found that at strong p + -doping the band structure of the InSb p-n junction has the form that can facilitate the emergence of additional mechanisms of current flow due to the tunneling and avalanche effects at the reverse bias. Using the literary data of the electron and hole lifetimes in InSb at cryogenic temperatures, we have found that the coefficient of bulk recombination can have an essential spatial dependence and considerably increases in the space charge region of p-n diode. The theory was applied to our analysis of p-n InSb diodes with p + -doping by using Be-ion implantation performed in ISP NASU. The theory predicts optimal conditions for detection of infrared emission. The technological process of fabrication, processing and testing has been described in details. Theoretically, it has been found that for parameters of the fabricated diodes and at 77 K the dark currents limited by diffusion and generation-recombination mechanisms should be less than 0.1 μA at the inverse bias of the order of 0.1 V. The measured diode’s I-V characteristics were expected to have strong asymmetry, however, dark currents are by one order larger than those predicted by theory. The latter can be associated with additional current mechanisms, namely: tunneling and avalanche effects

Strength of EU-level food environment policies and priority recommendations to create healthy food environments

Background Food environments impact on diets, obesity and non-communicable diseases (NCDs). Government policies are essential to create healthy food environments. This study aimed to assess the strength of European Union (EU)-level policies, and identify and prioritize actions for the EU to create healthy food environments.Methods The Healthy Food Environment Policy Index (Food-EPI) was applied. The Food-EPI included 26 policy and 24 infrastructure support indicators. Independent experts (n = 31) rated the strength of EU-level policies and infrastructure support for each of these indicators (on a 5-point scale, from very weak to very strong) and identified and prioritized actions to improve food environments.Results For 65% of the 26 policy indicators, EU-level policies were rated as weak and for 23% as very weak. For 63% of the 24 infrastructure support indicators, EU-level policies were rated as moderate and for 33% as weak. The experts recommended 18 policy and 19 infrastructure support actions to the EU. The Top 5 prioritized policy actions included three actions in the food composition domain (e.g. setting mandatory food composition targets), one action in the food prices domain and one action in the food promotion domain. The Top 5 prioritized infrastructure support actions included three actions in the leadership domain (e.g. developing a high-level NCDs Prevention Strategy) and two actions in the monitoring domain.Conclusions There is large potential for the EU to strengthen its policies and infrastructure support in order to improve food environments. This study specifies priority actions for the EU to create healthy food environments