475 Abstract: Theoretical treatment by analysis the Al0.3Ga0.7As/GaAs for long and short heterojunction diode is presented. The analysis is started by obtaining the built- in potential from the structure of diode, then the electric field and potential distribution are attained using different concentrations. In case of equal concentration, the maximum field is (4.32×10 4 V/cm) and potential with maximum peak at (1.2V), the depletion layer capacitance was also defined at applied voltage (VR) with value about (11.6x10 15 F/cm 2 ). According to the type of doping in (P-n) heterojunction the injected minority carrier and current densities analysis are achieved when applying voltage (+0.8 V) for forward bias and (-0.8 V) for reverse bias for both long and short diode, respectively. The value of minority carriers in n-side for both short and long diode is about (10.8X10 9 cm -3 ) at forward bias. The (I-V) characteristics for two diodes (long and short) is executed using the Drift-diffusion model. The resulting for the (I-V) characteristics show typical exponential relationship between the applied voltage and output current in Cartesian and semi-log plots. The complete modeling of the device is achieved by MATLAB software. 1. Introduction Semiconductor heterojunction produced by utilising two different semiconductor materials to build the junction, but when the same semiconductor materials utilised to build the junction the homojunction is obtained. The energy band of heterojunction will have a discontinuity at the junction interface due to the different materials that utilised to build the junction, this will cause an abrupt junction in which the semiconductor changes abruptly from wide-bandgap material to narrow-bandgap material or vice versa. In the case of the lattice constant of the two materials are perfectly matched, a useful heterojunction will have resulted. Since any mismatch in the lattice gives dislocations resulting in interface states. Gallium arsenide-aluminum gallium arsenide (GaAs/Al0.3Ga0.7As) junction have a lattice constant which vary by no more than 0.14 percent, therefore; the GaAs and Al0.3Ga0.7As system have been investigated quite thoroughly [1]. Heterojunction research was taken up intensively after 1957, when Kroemer suggested that anisotype heterojunctions might exhibit extremely high injection efficiencies in comparison with homojunctions. Since that time, Muneer A. Hashem 2 *Sarah K. Mohammed 1 1) M.Sc., Student Electrical Engineering Department, Mustansiriyah University, Baghdad, Iraq. 2) Assistant Prof., Electrical Engineering Department, Mustansiriyah University, Baghdad, Iraq. Journal of Engineering and Sustainable Development http://jeasd.uomustansiriyah.edu.iq https://doi.org/10.31272/jeasd.conf.1.53 AL0.3GA0.7AS/GAAS HETEROJUNCTION DIODE ANALYSIS *Corresponding author: sarahkadhim344@gmail.com First Online Scientific Conference for Graduate Engineering Students June 2020