Technique and setup for diagnostics of p-n junction–package thermal resistance in high-power gallium nitride LEDs

We present a setup and procedure of studying p-n junction–package thermal resistance in high-power light-emitting diodes (LEDs) from their thermal relaxation. A set of LEDs mounted on a metal-core printed circuit board (MCPCB) were studied. The contributions to the total thermal resistance from a heavy heat sink, MCPCB, heat slug and LED chip are separated

Temperature dependence of contact resistance of Au-Ti-Pd2Si-n+-Si ohmic contacts

We investigated temperature dependence of contact resistance of an Au-Ti-Pd2Si ohmic contact to heavily doped n+-Si. The contact resistance increases with temperature owing to conduction through the metal shunts. In this case, the limiting process is diffusion input of electrons to the metal shunts. The proposed mechanism of contact resistance formation seems to realize also in the case of wide-gap semiconductors with high concentration of surface states and dislocation density in the contact

Optically controlled 2D tunnelling in GaAs delta-doped p-n junction

A new type of an optically controlled tunnelling process in a specially designed Esaki diode is investigated. The additional peak appears due to tunnelling of 2D electrons accumulated at ground state of delta doped layers embedded nearby the p-n junction into the valence band of the p⁺-contact. It is found that the voltage position of an additional resonant peak shifts to lower bias voltage with increasing both incident light intensity and temperature. Our experimental data and theoretical simulations show that this shift is a result of an electrical field redistribution in the region of the p-n junction caused by non-equilibrium carriers generated with optic or thermal excitation

Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine 8 PACS 85

Abstract. We consider the features of formation of AuTiPd ohmic contacts to p + -Si. Metallization was made by vacuum thermal sputtering of Pd, Ti and Au films onto the Si substrate heated up to 330 С. It is shown that the contact resistivity increases with temperature; this is typical of metallic conductivity. We suggest that the ohmic contact is formed owing to appearance of shunts at Pd deposition on dislocations or other structural defects. The number of shunts per unit area is close to the measured density of structural defects at the metalSi interface

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Resonant spectroscopy of electric-field-induced superlattices

A system of interdigital gates is used to create a periodic potential profile in a multilayer heterostructure. The electrostatic problem for the spatial distribution of the potential is solved and experimentally examined by measurements of current-voltage characteristics of resonant-tunnelling diodes embedded in the depletion region of the Schottky contact. It is shown that the position of the resonant peak voltage is sensitive to the spatial potential distribution and that with appropriate parameters of the heterostructure the sensitivity of the gates can be considerably enhanced. (C) 2001 American Institute of Physics