Pressure On The Gaas-ga The <sub> 1-x </ Sub> Al <sub> The X </ Sub> The Nature Of The Shallow Donor Impurities Of As Symmetric Double Quantum Dot Impact

In the effective mass approximation , the binging energy and the density of shallow-donor impurity states in symmetrical GaAs-Ga_1-xAl_xAs double quantum dots are calculated variational using a parameter wave function. We have found that there are the effects of many factors on the binging energy of shallow-donor impurity states including the compressive stress, the size of quantum dots, the barrier width and the position of donor ion, and then the binging energy take place a complex variety.Firstly, we have calculated probability density of an electron when the donor impurity localed at the center of the barrier , the center of the right quantum dot of the symmetrical GaAs-Ga_1-xAl_xAs double quantum dots for two values of the applied stress, 10Kbar and 30Kbar, respectively the results obtained basically are a good show for the effect of compressive stress on the electronic probability distribution .Secondly, we calculate and discuss the binding energy of a donor impurity as a function of the growth direction donor oin position in symmetrical GaAs-Ga_1-xAl_xAs double quantum dots for the different values of the applied compressive stress.Thirdly, by considering the effect of effective mass and dielectric constant mismatch in the two materials, we show the role of the quantum size confinement in Fig.6, which the binding energy for different donor ion position as a function of the size of quantum dot in GaAs-Ga_1-xAl_xAs double quantum dots Simultaneously, by the same method, the effect of the central barrier width on the binding energy for different donor ion position and two values of theapplied compresslve stress are shown.In addition, the average distance between the donor ion and the electron as a function of the size of the quantum dot are also calculated, and the results are satisfactory.At last, we calculate the effects of the compressive stress on the binding energy of donor impurity for different donor ion position in GaAs-Gai -xAlxAs double quantum dots. Moreover, we obtain the shallow-donor binding energy as a function of the applied compressive stress in the limit in which the quantum dot turns into the quantum well. In this limiting case, our theoretical results are in good agreement with the previous results in quantum well.The results aie discussed in detail. The conclusion are as follows:(1) The effects of the quantum dot size on the binding energy of donor impunity states ate in good agreement with the ones from tUe previous theories and experiments. Due to the cmiplir-.- of;vc symmetrical GaAs-Gai .xAlxAs double quantum dots, we find that our results are smaller than those in single quantum dot.(2) By calculating the effects of the barrier width on the binding energy, in the limit of the large barrier width, we find that the binding energy converge to the binding energy value for the single quantum dot. In addition, the binding energy of the donor ion on the barrier edge increases until the barrier becomes sufficiently large as to impede the wave function penetration toward the second dot, and it has the smallest value in relation to the wave function infiltration.(3) The Fig.5 shows the binding energy of donor impurity as a function of the donor ion position. As can be seen, the binding enerev is much larger when the donor ion is located at the centre ofthe quantum dot than of the other donor positions. This is because the systematic wave function vanish at the boundaries and thus their contributions to the energy are smaller when the donor ion is at other positions.(4) We observe that the average distance between the donor ion and the electron decreases for small quantum dot sizes, until reaching a minimal value, and then increases with increasing quantum dot size as expected due to the weakness of the geometric confinement. It is consequent that the binding energy of a donor impurity yields a reduction as the average distance increases.(5) The compressive stress dependence of the binding energy for different impurity position in symmetrical GaAs-Gai.xAisA? double quantum dots is presented in the paper. As observed, forwith the str.is. For stress values greater than 13 5Kbar, the direct gap regime turn into the indirect gap regime, which is well known that the T-X crossover in GaAs, diminishing the barrier height with stress, causing the nonlinear variation observed in binding energy for all donor position.