Showing papers by "Jean Massies published in 2017"

Influence of the heterostructure design on the optical properties of GaN and Al0.1Ga0.9N quantum dots for ultraviolet emission

Abstract: The 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.

Photoluminescence properties of porous GaN and (Ga,In)N/GaN single quantum well made by selective area sublimation

Abstract: Porous GaN and (Ga,In)N/GaN single quantum well layers are fabricated using a selective area sublimation (SAS) technique from initially smooth and compact 2-dimensional (D) layers grown on Si(111) or c-plane sapphire substrates. The photoluminescence properties of these porous layers are measured and compared to reference non-porous samples. Whatever the substrate used, the porosity leads to an increase of the room temperature photoluminescence intensity. The magnitude of this increase is related to the initial defect density of the 2D epitaxial layers and to the degree of carrier localization prior to the SAS process.