Morphologies Of Self-assembled GaSb/GaAs Quantum Dots Prepared By MOCVD

The research on the GaSb/GaAs quantum dots have been done in recent yearsbecause of its special band structure, this structure is widely used in the near-infraredquantum dot lasers in optical fiber communications, mid-infrared detectors andphotovoltaic cells. The devices which have quantum dots structures can innovate itsperformance fundamentally. The GaSb/GaAs quantum dots structure was seen as oneof the most potential quantum dot structure owing to it can be widely used in thegroup Ⅲ-Ⅴ optoelectronic devices. The growth of self-assembled is a preparationmethod which is currently used for the growth of high-density, small size anddislocation-free quantum dots. This preparation method could make it compatiblewith traditional device technology so this method rapid development in the late1990s,and the S-K theory was widely accepted by researchers.In this thesis, LP-MOCVD epitaxial growth techniques was use to prepared theGaSb/GaAs quantum dot and the more conducive to the growth have been gotbecause the control precision of epitaxial growth could be improved at low pressure.In this paper, the trimethyl gallium（TMGa） and triethyl antimony （TESb） were usedas organic precursors to grow the self-assembled GaSb/GaAs quantum dots on the（100） planes of GaAs substrate. In the MOCVD growth parameters, the growthtemperature of GaSb/GaAs quantum dots have most obvios impact. The density ofthe quantum dots increased and then decreased with the temperature increasing, andthe maximum density appeard at500℃which the small islands density of³.5×10¹⁰cm^-2with the average width and height are32.2and3.6nm, respectively,in addition the Ostwald ripening islands density of¹.73×10¹⁰cm^-2with theaverage width and height are56.4and8.7nm, respectively. The pressure also havesome contribution on the growth of quantum dots, the quantum dots density of¹.6×10¹⁰cm^-2increased to6.0×10with the average width and heightof49.3nm⁶8.8nm and5.4nm⁹nm nm decreased to20.2nm²8.7nm and1.4nm⁶.3nm respectively when the pressure change from100mbar to400mbar.When Ⅴ/Ⅲ <1, it have no significant effect on the growth of quantum dots and thenthe quantum dots density of⁵.8×10¹⁰cm^-2with the average width and height are26.4and2.5nm, respectively. When Ⅴ/Ⅲ>1, the quantum dots size have increased,on the contrary, the density decline markedly due to changes in the mode of growth. The growth of GaSb/GaAs quantum dots, not only affected by MOCVD growthparameters, but also influenced by rapid growth time, interruption time andalternately growing cycles. The growth mode of the quantum dots are decided byrapid growth time, and the uniform size and high density quantum dots only grown inSK1mode zone. When the rapid growth time is6seconds and the quantum dots inthe SK1mode, quantum dots with an average diameter of20.5nm, an average heightof4.1nm, and a density of approximately, a density of about7.5×10¹⁰cm^-2.If therapid growth time is extended, the size of the quantum dots will be increased. And thedistribution of the quantum dots will be uneven, of lower density and anisotropy.There was no significant impact of the interruption time on the dimensions anddensity of the quantum dots, when the interruption time is extended from10s to20s,the average diameter of the quantum dots is elevated from27.3nm to38.3nm, theaverage height is reduced from7.3nm to5.2nm and density is reduced from8.4×10¹⁰cm^-2to6.2×10¹⁰cm^-2. Alternately growing cycles have a significantimpact on the growth of quantum dots, when the number of cycles increases, thedensity of the quantum dots will be increased from1.6×10¹⁰cm^-2to8.0×10¹⁰cm^-2, and the uniformity of size will be obviously improved.The high-density, small size and uniform distribution quantum dots will beobtain by researching the rule of the growth of GaSb/GaAs quantum dots byLP-MOCVD epitaxial growth techniques and thus can lay the foundation for the nextstep to improve the efficiency of quantum dot devices.