Fig. 2.8 (a), Fig. 2.14 (a) (b) (c) and Fig. 2.9 (b), Fig. 2.15 (a) (b) (c) show multifrequency C-V curves of MOSCAPs with a Al2O3 film on p- and n-type TMA treated (100)-oriented In0.53Ga0.47As after post-metallization FGA under different PDA conditions, respectively, measured at 300K. For p-type, the MOSCAPs with PDA at 500 oC for 120 s exhibit the worst electrical characteristics. Although the capacitance value at VG= -2 volts of MOSCAPs with PDA 500 oC for 120 s is the largest, the frequency dispersion of the samples with PDA 500 oC for 120 s severely degrades not only near accumulation (ΔC (@VG = -2 V) =16.91%) but also in depletion. It is noted that the response of interface traps at VG= 0 to VG= 1 volt is severely getting large as the temperature of PDA increases; therefore, for our In0.53Ga0.47As substrate, the limited temperature of post deposition annealing is 300 oC. The minority carrier response of MOSCAPs with PDA 500 oC for 120 s is obviously seen at VG= 1 to VG=2 volts. For the n-type MOSCAPs, the frequency dispersion of MOSCAPs with PDA 500 oC for 120s is 8.99% larger than MOSCAPs with other PDA conditions. All the samples under various PDA conditions demonstrated the response of interface states at negative gate voltages due to bias-dependent and frequency-dependent capacitance. All of the frequency dispersion values under various PDA conditions are summarized in Table 2.1.
Fig. 2.10 (a), Fig. 2.16 (a) (b) (c) and Fig. 2.11 (b), Fig. 2.17 (a) (b) (c) show conductance maps of Al2O3/TMA-treated In0.53Ga0.47As MOSCAPs with FGA under different PDA conditions, on both p- and n-type (100)-oriented In0.53Ga0.47As, respectively, at temperature 300K. These maps show the magnitude of normalized
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conductance (G/ω)/Aq as a function of ac frequency f and the gate voltage VG. For the p-type MOSCAPs, all plots show that a distinct signal exists at the positive gate voltage and lower frequency. The color variation in this region is getting dramatic as the temperature of PDA is above 400 oC. We speculate that the amount of interface states considerably increases as the temperature of PDA is getting higher. For the plot of PDA 500 oC for 120 s, there is an additional signal existing at gate voltage between -2 and -1 volt and higher frequency; furthermore, we also observe that the conductance is constant at gate voltage between 1 and 2 volts, indicating minority carrier response. For the n-type MOSCAPs, there is a conspicuous variation in color appearing at the negative gate voltage in all graphs, which implies that energy loss is dramatically rising. Similarly, the G-V response to this energy loss is made by interface states owing to its gate-voltage dependent and frequency-dependent conductance. Additionally, the signal existing between VG= 1 and VG= 2 volts and higher frequency becomes distinct as the temperature of PDA increases.
Fig. 2.18 (a) (b), and (c) show X-ray photoelectron spectroscopy of ALD-TMA (10 cycles)/Al2O3 (10 cycles) on (100)-oriented In0.53Ga0.47As with post-metallization FGA under various PDA conditions. XPS scans of Ga 2p3/2, In 3d5/2, and As 2p3/2 core levels are taken. From Fig. 2.18 (a) and (b), we observe that there is no significant change in Ga 2p3/2 and In 3d5/2 spectra. The As 2p3/2 spectra, shown in Fig. 2.18 (c), demonstrates that As-As bonds are present in these PDA conditions. It is noted that the concentration of As-As states dramatically increases under PDA 500 oC. We also find that a lower binding energy peak, which is labeled As- in the spectra, is detected on the samples with PDA 500 oC for 120s. This may be an indication of breaking of As-As states at the surface, creating an arsenic dangling bond. In addition, the ratio of As2O3 to As2O5 at PDA 500 oC is the lowest. Table 2.3 shows the ratio of the fitted area of the As-As and As- components and As2O3 to As2O5 from the As 2p3/2 spectra
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for the In0.53Ga0.47As (100).
The results suggest that the considerable existence of As-As states or As- states and As2O5 at the interface should be avoided, causing the degradation of electrical characteristics. The reason for the degradation of C-V characteristics with PDA 500
oC for 120 s may be the precipitation of arsenide and lower ratio of As2O3 to As2O5 (As2O3 to As2O5). High temperature annealing results in the excess arsenic atoms produced either the decomposition of In0.53Ga0.47As itself or the chemical transformation of the oxide species through reactions with the In0.53Ga0.47As channel layer. The elemental arsenide overlayer acted as a metallic contamination source nearby the interface between oxide and substrate increases the surface recombination velocity, deteriorating insulator properties [36]. In addition, the possibility that a little amount of arsenic oxides diffused into the Al2O3 during post deposition annealing at temperature above 300 oC cannot be excluded.
2.4 Electrical Characteristics of ALD-TMA/In
0.53Ga
0.47As (111)A and Interfacial Chemistry
There have been few studies regarding the MIS properties on the (111) surface of III-V semiconductors. Some previous research showed that the electrical characteristics of (111)A-oriented In0.53Ga0.47As and (111)A-oriented GaAs MIS capacitors with Al2O3 dielectrics deposited by ALD were comparable to or even better than those on the (100)-oriented In0.53Ga0.47As and (100)-oriented GaAs MIS capacitors [37-39]. Besides, since the former approach has succeeded in forming uniform and dislocation-free InGaAs layers on Si (111), the characteristics of
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MISFET on the (111)-oriented InGaAs are of great interest [40].
Fig. 2.19 (a) (b) (c) (d) show multifrequency C-V curves of MOSCAPs with a Al2O3 film on p-type TMA treated (111)A-oriented In0.53Ga0.47As after post-metallization FGA under different PDA conditions, measured at 300K. The frequency dispersion at VG= -2 slightly improves at PDA of 300 oC and 400 oC but degrades at PDA of 500 oC, shown in Table 2.2. At positive gate bias, the capacitance remarkably increases at lower frequency compared to our previous C-V curves of p-type In0.53Ga0.47As MOSCAPs with (100) orientation, shown in Fig. 2.8 (a) and Fig.
2.14 (a) (b) (c). We suppose that the inversion response appears at more positive gate voltages and lower frequency due to the constant capacitance.
Fig. 2.20 (a) (b) (c) (d) show conductance maps of Al2O3/TMA-treated In0.53Ga0.47As MOSCAPs with FGA under different PDA conditions, on p-type (111)A-oriented In0.53Ga0.47As at temperature 300K. These maps show the magnitude of normalized conductance (G/ω)/Aq as a function of ac frequency f and the gate voltage VG. Under various PDA conditions with FGA, we could easily observe the minority carrier response at more positive gate bias in all graphs, and the as-deposited one with FGA demonstrates the strongest minority carrier response. The response of interface states also exists at gate voltage between -1 and 0 volt.
Fig. 2.21 (a) (b), and (c) show X-ray photoelectron spectroscopy of ALD-TMA (10 cycles)/Al2O3 (10 cycles) on (111)A-oriented In0.53Ga0.47As with
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shows the ratio of the fitted area of the As-As and As- components and As2O3 to As2O5 from the As 2p3/2 spectra for the In0.53Ga0.47As (111)A.