Investigations on Relieving Kink Effects of InAlAs/InGaAs High Electron Mobility Transistors

Autor: Jun-Chin Huang, 黃俊欽
Rok vydání: 2007
Druh dokumentu: 學位論文 ; thesis
Popis: 95
In this dissertation, we have successfully fabricated and investigated InAlAs/InGaAs high electron mobility transistors (HEMT’s) by employing different InxGa1-xAs channel designs and fabrication processes to improve the breakdown voltage and power characteristics. First, an InP etch stop layer was inserted on top of the InAlAs Schottky layer to improve the surface traps on the InAlAs layer and to alleviate the kink effects. Because increasing the carrier transport property and the threshold field for impact ionization in a linearly-graded channel structure, the LGC-HEMT has demonstrated high device gain of 342 mS/mm, high current drive capability of 360 mA/mm, low gate leakages of -2.0 μA/mm at VDS = 2V, low output conductance of 3.9 mS/mm, high voltage gain of 94.2, high output power of 12.43 dBm, and good thermal stability, as compared to those of the LMC-HEMT and ILGC-HEMT, respectively. Then, we’ve investigated the double ��-doped In0.425Al0.575As/In0.425Ga0.575As MHEMT’s. Since the energy band-gap of In0.425Ga0.575As channel is wider than that of the In0.53Ga0.47As channel in lattice-matched InP HEMT devices, the impact ionization phenomenon within the channel is expected to be reduced, thus relieving the kink effects. Consequently, the proposed double ��-doped MHEMT has shown low output conductance of 0.73 mS/mm, improved gate-drain breakdown voltage of -19.2 V, voltage gain of 402 and saturated output power of 18.28 dBm. Besides, the proposed MHEMT has also demonstrated superior high-temperature performance up to 500 K with positive thermal threshold coefficient (�gVth/�gT) of 0.39 mV/K. To facilitate the high-frequency applications, we have further investigated a ��-doped In0.45Al0.55As/InxGa1-xAs MHEMT by using a linearly-graded InxGa1-xAs (0.63→0.53) channel. Due to the high indium composition of the InxGa1-xAs channel, better carrier transport characteristics have been obtained to improve the transconductance and high-frequency characteristics. We have used the SiNx surface passivation and double-recess techniques to relieve the above-mentioned kink effects. Therefore, the propose MHEMT device has improved the extrinsic transconductance (gm) from 419 to 445 mS/mm, breakdown voltage from -7.7 to -13.1 V, output conductance (gd) from 17.7 to 6.3 mS/mm, voltage gain (AV) from 29 to 69, cut-off frequency (ft) from 55 to 61 GHz and maximum oscillation frequency (fmax) from 92 to 108GHz, the output power (Pout) from 14.33 to 18.91 dBm and the third-order intercept point (OIP3) from 19.3 to 28.2 dBm at 300 K, respectively. In addition, the device with double gate-recess has also demonstrated improved thermal stability with the deviations of gm,max and ID,max from 300 K to 500 K are only 18.8 % and 12.6 %, respectively. In addition to using the SiNx surface passivation and double-recess techniques, we’ve further investigated to relieving kink effects by using the ozone water oxidation treatment. The gate oxidation process provides a cost-effective method to deposit an about 8-nm thick oxide film with superior surface flatness in the gate structure of the MOS-MHEMT. In comparison, the proposed MHEMT with the ozone treatment has demonstrated improved peak gate leakage density from 59.5 μA/mm to7.1 μA/mm, breakdown voltage (BVGD) from -5.8 V to -14.9 V, output conductance (gd) from 33.1 to 4.5 mS/mm, voltage gain (Av) from 11.7 to 80.5, gate-voltage swing (GVS) from 0.45 to 0.9 V, output power (Pout) from 13.43 to 18.34 dBm and OIP3 from 15.8 to 26.1 dBm at 300 K, respectively.
Databáze: Networked Digital Library of Theses & Dissertations
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