Abstract:Avalanche photodiode (APD) has been intensively investigated as a promising candidate to replace the bulky and fragile photomultiplier tubes (PMT) for weak light detection. However, intrinsic limits in semiconductors make the former still inferior to the latter on device performance up to now. In conventional APDs, a large portion of carrier energy drawn from the electric field is thermalized, and the multiplication efficiencies of electron and hole are low and close. In order to achieve high gain, the device has to work under breakdown bias, wherein carrier multiplication proceeds bi-directionally to form a positive feedback multiplication circle. In this case, APDs should work under Geiger mode as a compromise between sustainable detection and high gain. On the other hand, PMT can achieve stable high gain under constant bias (linear mode). Here, we demonstrate an APD works like a PMT, which means it can work under constant bias and holds high gain without breakdown simultaneously. The device is based on a GaN/AlN periodically-stacked-structure (PSS). For the PSS holds the intrinsic features that there are deep Γ valleys and larger band offset in conduction band, electron encountered much less scatterings during transport in PSS APD. Electron holds much higher efficiency than hole to draw energy from the electric field, and avalanche happens uni-directionally with high efficiency. Extremely high ionization coefficient (3.96×10 5 /cm) of electron and large ionization coefficient ratio (over 100) between electron and hole is calculated in the PSS APD by Monte-Carlo simulations and a recorded high gain (10 4 ) tested under constant bias without breakdown is obtained in a prototype device, wherein the stable gain can be determined by the periodicity of the GaN/AlN PSS and no quenching circuits are needed for sustainable detection. This work not only brings a new light into avalanche multiplication mechanism, but also paves a technological path to realize highly sensitive APD working under constant bias like PMT.Keywords: Avalanche photodiode; GaN; Ionization; Periodically stacked structure; Transport Introduction:

International audienceThe optical properties of AlyGa1-yN quantum dots (QDs), with y 1⁄4 0 or y 1⁄4 0.1, in an AlxGa1 xN matrix are studied. The influence of the QD layer design is investigated pointing out the correlations between the QD structural and optical properties. In a first part, the role of the epitaxial strain in the dot self-assembling process is studied by fabricating GaN QD layers on different AlxGa1 xN layers with 0.5 x 0.7. Photoluminescence (PL) measurements show the main influ- ence of the increase of the internal electric field (Fint) on the QD optical response inducing a strong red shift in the emission energy as x increases. Time resolved combined with temperature depen- dent PL measurements enabled the estimation of the QD internal quantum efficiencies at low tem- perature showing values around 50%. In addition, a PL integrated intensity ratio up to 74% is shown, between 300 and 9 K. In the second part, the design of Al0.1Ga0.9N QDs was investigated, by varying the Al0.1Ga0.9N amount deposited. An increase of the transition energy (from 3.65 eV up to 3.83eV) is obtained while decreasing the deposited amount. Calculations of the ground state transition energies as a function of the Al0.1Ga0.9N dot height give a value of Fint around 2.060.5MV/cm. Therefore, the propensity of Al0.1Ga0.9N dots to emit at much higher energies than GaN dots (a PL shift of 1 eV using a low excitation power) is seen as the consequence of the reduced Fint together with their smaller sizes

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