Abstract
可見光源在雷射印表機及光纖通訊上有其重要的地位，尤其在全色彩顯示器(Full Color Display)更是有重大的應用。人類眼睛對於波長為555 nm的純綠光有最大的靈敏度，因而我們研製的磷化鎵/磷化鋁鎵雙異質結構發光二極體，其發光波長為558 nm，非常接近555nm，所以當作光源非常適。本論文以液相磊晶法成長磷化鎵 (GaP)和磷化鋁鎵 (AlGaP)晶膜於磷化鎵 (GaP)基板上，進而成長多層晶膜以研製雙異質結構之綠光發光二極體。我們先研究未摻雜磊晶層的光電特性，再分別研究摻雜碲(Te)及鎂(Mg) 的磊晶層之光電特性-載子濃度分佈及光激光譜強度。利用平衡溫度法來成長未摻雜之磷化鎵及磷化鋁鎵磊晶層，其各有3×1016 cm-3和3.5×1016 cm-3之載子濃度。從C-V量測知當磷化鎵 (GaP) 磊晶層以Mg為p型摻雜，其電洞的濃度由 1.6×1016 cm-3 至 3×1018 cm-3。當磷化鋁鎵(Al0.3Ga0.7P)磊晶層以Te為n型摻雜，其電子濃度由 4.7×1017 cm-3至 7×1018 cm-3；當磷化鋁鎵 (Al0.3Ga0.7P) 磊晶層以Mg為p型摻雜，其電洞的濃度由1.6×1017cm-3至1.8×1018cm-3。另外我們分析未摻雜及摻雜Mg和Te之磷化鎵及磷化鋁鎵磊晶層的光激光譜，在低溫下，主要出現一個強的尖峰及兩個較弱的尖峰，均由施體(donor)到受體(acceptor)的覆合所組成。最後，我們選擇適當的摻雜濃度，成功地研製出雙異質結構之綠光發光二極體。此元件經由特性量測，得到良好的電流-電壓 (I-V)及電激光譜(Electroluminescence)特性。由電流-電壓(I-V)特性曲線得知，順向切入電壓(turn-on volatge)約為1.04V，理想因素約為1.51。由電激光譜(EL)知在電流為20毫安培時的發光波長為558nm。Recently, visible light sources in the short wavelength regionhave many attractive applications in full color display,optical information- processing systems such as optical diskmemories and optical fiber communication systems with pla- sticfibers. For human vision, the relative eye sensitivity has themaximum value in the location of λ=555nm (pure green light) .Because the large energy gap of GaP is 2.26eV at roomtemperature, the green radiative recombination may be obser-ved in this material. Near pure green light-emitting diodeshave been obtained from GaP/AlGaP double hetero-junctionstruct- ures. In this paper, we report the growth of n-Al0.3Ga0.7P, p- GaP and p-Al0.3Ga0.7P epitaxial layers on (111)B GaPsub- strate from a fixed melt composition by LPE technique. Atfirst, we study the electrical and optical properties ofundoped-GaP and Al0.3Ga0.7P, then study the epitaxial layers ofTe- or Mg- doped GaP and Al0.3Ga0.7P.The lowest carrierconcentration of undoped GaP epitaxial layer is 3×1016 cm-3measured by a mercury probe C-V method. It is grown at 952℃and cooling rate of 0.5℃/min. The lowest carrier concentrationof undoped Al0.3Ga0.7P epitaxial layer is 3.5×1016 cm-3. It isgrown at 950℃ and cooling rate of 0.5℃/min.The carrierconcentrations of GaP are from 1.6×1016cm-3 to 3×1018 cm-3for p-type doped and from 2×1017 cm-3 to 2×1018 cm-3 for n-type do- ped, respectively. Finally, we grow three layers in asingle run to fabricate double heterojunction p-Al0.3Ga0.7P/p-GaP/n- Al0.3Ga0.7P green LEDs.LEDs are characterized by thecur- rent-voltage (I-V) and electro-luminescence (EL)measureme- nts . A forward-bias turn-on voltage of 1.0447 Vwith an idea- lity factor of 1.51 are obtained from the current-voltage meas- urements.The wavelength of EL emission peak isaround 558 nm at an operating current 20mA at room temperature.The external quantum efficiency of this device is about4.35×10-3﹪.