N. Yıldırım

On temperature-dependent experimental I-V and C-V data of Ni/n-GaN Schottky contacts

We report the current-voltage (I-V) and capacitance-voltage characteristics (C-V) of Ni/n-GaN Schottky diodes. Gallium nitride is a highly promising wide band gap semiconductor for applications in high power electronic and optoelectronic devices which require Schottky barriers for modulating the channel mobile charge. The I-V and C-V characteristics of the diodes have been measured in the temperature range of 80–400 K with steps of 20 K. Thermal carrier concentration and barrier height versus temperature plots have been obtained from the C−2-V characteristics, and a value of α=−1.40 meV/K for temperature coefficient of the barrier height. The modified activation energy plot according to the barrier inhomogeneity model has given the Richardson constant A∗ as 80 or 85 A/(cm2 K2).

The interface state density characterization by temperature-dependent capacitance–conductance–frequency measurements in Au/Ni/n-GaN structures

We have fabricated the Au/Ni/n-GaN structures and measured their capacitance–frequency (C–f) and conductance (G/w)-angular frequency (w) characteristics in the temperature range of 60–320 K. The C–f curves for different reverse bias voltages have shown a behavior almost independent of the bias voltage at frequencies above 300 kHz at each measurement temperature. We have calculated the temperature-dependent interface state density, Nss, values from the G/w versus w curves. The Nss value for the Ni/n-GaN interface ranges from 3.36 × 1011 cm−2 eV−1 at 0.0 V to 2.92 × 1011 cm−2 eV−1 at 0.40 V for 60 K, and 6.63 × 1011 cm−2 eV−1 at 0.0 V to 3.87 × 1011 cm−2 eV−1 at 0.40 V for 320 K. That is, the interface state density value increases with increasing temperature. It has been seen that the values of Nss obtained from the G/w versus w curves of the device are lower than the given values for metal/n-type GaN interface in the literature.

THE CHARACTERISTIC DIODE PARAMETERS IN Ti/p-InP CONTACTS PREPARED BY DC SPUTTERING AND EVAPORATION PROCESSES OVER A WIDE MEASUREMENT TEMPERATURE

The titanium/p-indium phosphide (Ti/p-InP) Schottky diodes (SDs) have been prepared by thermal evaporation and DC magnetron sputtering deposition. Then, their current–voltage (I–V) characteristics have been measured in the sample temperature range of 100–400K with steps of 20K. The characteristic parameters of both Ti/p-InP SDs have been compared with each other. The barrier height (BH) values of 0.824 and 0.847 at 300K have been obtained for the sputtered and the evaporated SDs, respectively. This low BH value for the sputtered SD has been attributed to some defects introduced by the sputtered deposition technique over a limited depth in to the p-type substrate. The BH of the evaporated and sputtered diodes has decreased with the standard deviations of 58 and 64mV obeying to double-Gaussian distribution (GD) in 220–400K range, respectively, and it has seen a more sharper reduction for the BHs with the standard deviations of 93 and 106 mV in 100–220K range. The Richardson constant values of 89.72 and 53.24A(Kcm)−2 (in 220–400K range) for the evaporated and sputtered samples, respectively, were calculated from the modified ln(I0/T2)−q2σs2/2k2T2 vs (kT)−1 curves by GD of the BHs. The value 53.24A(Kcm)−2 for the sputtered sample in high temperatures range is almost the same as the known Richardson constant value of 60A(Kcm)−2 for p-type InP.

CURRENT–VOLTAGE CHARACTERISTICS OF THERMALLY ANNEALED Ni/n-GaAs SCHOTTKY CONTACTS

The Schottky barrier type Ni/n-GaAs contacts fabricated by us were thermally annealed at 600∘C and 700∘C for 1min. The apparent barrier height Φap and ideality factor of the diodes were calculated from the forward bias current–voltage characteristic in 60–320K range. The Φap values for the nonannealed and 600∘C and 700∘C annealed diodes were obtained as 0.80, 0.81 and 0.67eV at 300K, respectively. Thus, it has been concluded that the reduced barrier due to the thermal annealing at 700∘C promises some device applications. The current preferentially flows through the lowest barrier height (BH) with the temperature due to the BH inhomogeneities. Therefore, it was seen that the Φap versus (2kT)−1 plots for the nonannealed and annealed diodes showed the linear behavior according to Gaussian distributions.

Characteristic diode parameters in thermally annealed Ni/p-InP contacts

The Ni/p-InP Schottky diodes (SDs) have been prepared by DC magnetron sputtering deposition. After the diode fabrication, they have been thermally annealed at 700℃ for 1 min in N 2 atmosphere. Then, the current-voltage characteristics of the annealed and non-annealed (as-deposited) SDs have been measured in the measurement temperature range of 60-400 K with steps of 20 K under dark conditions. After 700℃ annealing, an improvement in the ideality factor value has been observed from 60 to 200 K and the barrier height (BH) value approximately has remained unchanged in the measurement temperature range of 200-400 K. The BH of the annealed diode has decreased obeying the double-Gaussian distribution (GD) of the BHs with decreasing measurement temperature from 200 to 60 K. The BH for the as-deposited diode has decreased with decreasing temperature obeying the single-GD over the whole measurement temperature range. An effective Richardson constant value of 54.21 A/cm 2 K 2 for the as-deposited SD has been obtained from the modified Richardson plot by the single-GD plot, which is in very close agreement with the value of 60 A/K 2 cm 2 for p-type InP. The series resistance value of the annealed SD is lower than that of the non-annealed SD at each temperature and approximately has remained unchanged from 140 to 240 K. Thus, it can be said that an improvement in the diode parameters has been observed due to the thermal annealing at 700℃ for 1 min in N 2 atmosphere.

The Effects of Thermal Annealing and Sample Temperature on Current-Voltage Characteristics of Au/n-Si/Al Schottky Diodes

Gunumuz elektronik teknolojisinde ve elektronik sanayinde cok fazla kullanilan Schottky kontaklar genis bir uygulama alanina ve onemli bir yere sahiptir. Bu sebeple bu elemanlar uzerinde cok fazla durulmasi gerekir ve bircok arastirmanin da konusu olmustur. Diyodun tavlama ve numune sicakligiyla karakteristik parametrelerinin degisip degismediginin degisimini gormek icin diyotlarin tavlamaya ve numune sicakligina bagli akim-gerilim karakteristikleri incelendi. Yapilan hesaplamalar sonucunda tavlanmamis diyot icin oda sicakliginda idealite faktoru ve engel yuksekligi I-V olcumlerinden sirasiyla 1,15 ve 0,74 eV degerleri elde edildi. Yine 200 0 C tavlanmis diyot icin oda sicakliginda idealite faktoru ve engel yuksekligi sirasiyla 1,11 ve 0,73 eV olarak hesaplanmistir. Buna gore tavlama neticesinde diyot tavlama sicakligina bagli olarak daha kararli hale geldigi soylenebilir. Bu durum, metal yariiletken arayuzeyindeki istenmeyen fazlarin tavlama sicakligina bagli olarak azaldiginin veya buyuk olcude yok oldugunun bir kanitidir. Au/n-Si/Al Schottky diyotlarin oda sicakliginda tavlanmadan once ve 200 0 C’de tavlandiktan sonra seri direnc ve engel yuksekligi degerleri Norde Fonksiyonlari kullanilarak hesaplandi.