The GaAs/AlGaAs single quantum well (SQW) samples with nonintentionally doped confining layers were studied using deep level transient spectroscopy (DLTS) and capacitance-voltage-temperature. A sizeable DLTS signal was observed and believed to be from the thermal emission of the well electrons. However, it was found that the major signal peak was accompanied by two subpeaks and thus the QW must be a multilevel trap state. Different combinations of reverse voltage and fill pulse height allowed a DLTS study of the region before, within, and beyond the well location. Such an observation, in conjunction with the use of undoped AlGaAs barrier layers, proved that the DLTS signal is indeed from the well because it was only significant when probed within the well region and the assumption of the DX centers in some previous studies can be excluded. The fact that classically derived activation energy is close to the estimated band-gap discontinuity value and the carrier distribution centered at the geometric QW at room temperature revealed that the quantization effect was of second order. However, the detected activation energy depends on the testing conditions that precludes the determination of the band offset using the DLTS technique.
Interfacial microstructure and electrical properties of the Pt/Ti ohmic contact in pIn0.53Ga0.47As formed by rapid thermal processing Ho~e trap ~evel in Pt~Tilp~lnGa.As/nmlnP heterostructures due to rapid thermal processing Low-resistance ohmic contacts of Pt/Ti to p-InGaAsln-InP heterostructures were formed by rapid thermal processing (RTP). Deep level transient spectroscopy and current-voltage temperature (I-V-T) measurements were used to characterize this system in order to evaluate the stability of the Pt/Ti ohmic contact and the effects of different RTP temperatures on the device performance. A new hole trap level with activation energy of 0.89 eV was found in samples treated at temperatures above 500"C but not in those treated at lower temperatures. This trap, featured by a higher density when closer to the junction, was thought to be caused by Ti interdiffusion at high RTP temperature, in agreement with the analysis from Auger depth profiling. Four electron trap levels with activation energies of 0.61, 0.45, 0.35, and 0.30 cV were observed for all samples and believed jo be native defects in InP.f-V-T measurements revealed current mechanisms independent of the RTP temperatures indicating that the new hole trap does not influence current conduction mechanisms.The Pt/Ti low-resistance nonalloyed ohmic contacts have been successfully used on p-InGaAspl and pInGaAs.2 Rapid thermal processing (RTP) at 450°C for 30 s yielded the lowest specific contact resistance of 3.4X 10 8 n cm 2 to p-InGaAs. Auger electron spectroscopy CABS) with depth profiling revealed the interfacial reaction between Ti, As, and In to form the very low contact resistance. The reaction at 450°C was relatively moderate. However, at 500 °C or higher temperatures, the outdiffusion of In and interdiffusion of Ti were more pronounced and caused an increase in contact resistance. A similar study was recently done on p-GaAs 3 and InAs.4 A deep level due to Ti as a dopant was found in liquidencapsulated crystal (LEC) InP at 0.63 eV below the conduction band and was attributed to a Ti 4 . .,-ITi] t donor level. 5 Photoluminescence (PL) 6 and admittance spectroscopy 7 have been utilized to characterize the deep level defects for InGaAs/lnP heterostructures. However, little work has been done using deep level transient spectroscopy (DLTS) for this structure, especially when reacted by the R Til technique. background pressure better than 1 X 10 -7 Torr. Rapid thermal processing was carried out under ambient forming gas at temperatures between 300 and 600 cC in steps of 50 "C and duration of 30 s. The back surface ohmic contact was thermally evaporated using Au:Ge/Ni with a background pressure of 3 X 10-(, Torr, followed by RTP at 400°C for only 10 s in order to minimize any influence on the front contacts. The mesa diodes were defined using H3P04:H202:H20 = 1:8:20 etching solution, which gave a smooth etching rate of 0.11 JLm/min. Most of the diodes exhibited good rectifier characteristics. The samples were then numbered as 01 to 08 in sequence from t...
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